Actions

In Dungeons & Dragons, actions are basically the things that your character can do. Actions matter the most in combat, where there are stricter rules about what you can and can't do during your turn. Outside of combat situations, there is no turn order, and consequently much more lax rules about what you can and can't do in a single action.
==Combat==
During combat, you can generally perform a movement action (wherein you can move around the battlefield up to the amount determined by your character's speed) and a standard action in a given turn. Some actions are full-round actions, meaning they take up your entire turn. Others are free actions or swift actions, the former of which you can do for free during a turn (within reason) and the latter of which takes shorter than a movement action or a standard action, but you can only do one per turn -- and only certain actions can be done as a swift action.
d20srd has an excellent list of action types and what actions are commonly of that type. Listed below are how to actually perform those actions.
==Attacking==
Attacking with a physical (i.e. non-spell) attack requires two rolls; what you roll for a given attack is based on what kind of attack you're doing.
For melee attacks, you first roll a d20 + Base Attack Bonus + Strength mod (OR Dexterity mod, if your weapon or selected feats allow for it).
If your attack hits (i.e. your roll equals or exceeds the target’s AC), then you roll for damage. Every weapon has an associated damage roll for it (e.g. a Greatsword has 2d6). You roll that dice and add your Strength modifier to it. Two-handed melee weapons (e.g. greataxes, greatswords) add you 1.5x your Strength bonus, rounded up (e.g. 3 becomes 5) instead of just the flat Strength bonus.
For ranged attacks, you first roll a d20+ Base Attack Bonus + Dexterity mod. This includes throwing a weapon (e.g. throwing a dagger).
If your attack hits (i.e. your roll equals or exceeds the target’s AC), then you roll for damage. Every weapon has an associated damage roll for it (e.g. a light crossbow is 1d8). You roll that dice and do not add anything to it unless your weapon or feats specifically call for it. Thrown weapons will add your Strength modifier to the damage done.
There are also numerous "Special Attacks" you can perform, such as Grapples, Bull Rushes, or Disarms. Use this list to familiarize yourself with them.
==Initiative==
When combat starts, you roll for Initiative to determine turn order.
Initiative rolls are d20 + Dex mod. Some circumstances or feats may give bonuses to initiative rolls either for players or the enemies, such as "This player noticed the enemies first, so they get +3 to their Initiative roll".
There exists a round of combat called "the surprise round," which happens at the very beginning of the fight. Basically, ambushes occur during the surprise round. Only creatures aware of the hostile enemies will be able to act during the surprise round. After the surprise round ends, turn order goes to regular Initiative-determined order.
==Attacks of Opportunity==
During combat, sometimes you or the enemy may be permitted to attack outside of the turn order. This is called an attack of opportunity. The most common reason that attacks of opportunity happen is because someone ran through an area that an enemy "threatens" (which is almost always any area directly adjacent to where they're standing) or rolled a natural 1 while attacking an enemy. If this occurs, the enemy -- or you! -- will be allowed to attack whoever is susceptible to the attack of opportunity. This doesn't make you lose your turn or incur any penalties, so always make use of attacks of opportunity when the DM tells you that you can!
==Skill Checks==
When you want to use one of your character’s skills, such as Knowledge (Local) or Sense Motive, you make a skill check. Every skill has an associated ability with it, listed next to that skill on the character sheet (e.g. Sense Motive’s governing ability is Wisdom and Knowledge (Local)’s is Intelligence).
Skill checks are done by rolling a d20 + Ranks in that skill + associated Ability mod. If your roll equals or surpasses the DC (Difficulty Class) associated with what you’re trying to do, then your skill check succeeds. DCs are not publicly known to players to prevent players from knowing what they need to roll in order to succeed. Favorable or unfavorable circumstances can lower or raise the DC depending on what’s happening, so be mindful of your surroundings.
Player characters can help each other on Skill Checks, such as a second player character also using Bluff to make the first one's lie more credible.
For some skill checks, the DM may do the roll instead so you don’t know if it succeeded or failed.
You can choose to "take 10" or "take 20" on skill checks. d20srd explains it as follows:
Taking 10: When your character is not being threatened or distracted, you may choose to take 10. Instead of rolling 1d20 for the skill check, calculate your result as if you had rolled a 10. For many routine tasks, taking 10 makes them automatically successful. Distractions or threats (such as combat) make it impossible for a character to take 10. In most cases, taking 10 is purely a safety measure —you know (or expect) that an average roll will succeed but fear that a poor roll might fail, so you elect to settle for the average roll (a 10). Taking 10 is especially useful in situations where a particularly high roll wouldn’t help.
Taking 20:
When you have plenty of time (generally 2 minutes for a skill that can normally be checked in 1 round, one full-round action, or one standard action), you are faced with no threats or distractions, and the skill being attempted carries no penalties for failure, you can take 20. In other words, eventually you will get a 20 on 1d20 if you roll enough times. Instead of rolling 1d20 for the skill check, just calculate your result as if you had rolled a 20.
Taking 20 means you are trying until you get it right, and it assumes that you fail many times before succeeding. Taking 20 takes twenty times as long as making a single check would take.
Since taking 20 assumes that the character will fail many times before succeeding, if you did attempt to take 20 on a skill that carries penalties for failure, your character would automatically incur those penalties before he or she could complete the task. Common "take 20" skills include Escape Artist, Open Lock, and Search.
==Ability Checks==
Sometimes you may want to perform an action that is logical enough but doesn’t have an associated skill with it (e.g. trying to break down a door, trying to remember something). In that case, you roll an Ability check.
Ability checks are done like skill checks, except your roll is just d20 + Ability mod. The DM will tell you what ability mod you’ll be using when you perform your action.
Favorable or unfavorable circumstances can lower or raise the Ability check’s DC depending on what’s happening, so be mindful of your surroundings.
For some Ability checks, the DM may do the roll instead so you don’t know if it succeeded or failed.
You can take 10 or take 20 on Ability checks like you can for skill checks (e.g. Repeatedly bashing a door until it breaks down).
==Casting Spells==
Most spells do not have accuracy components like regular attacks do. If your spell does not say to roll for an accuracy check, then you can roll immediately to see its damage (if it’s a damaging spell) or effect (if, for example, it’s a Summon Monster spell that has you roll 1d3 to see how many monsters you summon). All spells that require such a roll will tell you what roll to perform.
Spells generally automatically will be cast immediately without requiring a roll. However, if your character is currently distracted in some way (e.g. is under attack, is being grappled, etc), then you may have to roll a Concentration skill check to see if you successfully cast the spell.
Some spells have "invisible" rolls that the DM performs to see if the spell is negated (such as a Will save) or doesn’t work as intended. Other circumstances may require you to roll to see what the spell does or how potent it is. You’ll be notified of this on a case-by-case basis if your spell does not normally require such a roll.
==Using Abilities==
Abilities like racial abilities or class abilities generally behave like spells and do not require an accuracy or check roll. You simply have to announce that you’re using them for them to take effect (e.g. Oscare uses Battle Howl).
Some class or racial abilities are passive, meaning you do not have to notify the DM of your use of them. They are permanently active on your character (barring unusual circumstances, such as an alova being blinded and thus losing her Spot bonus).
Any abilities that require a roll to check if they succeed will be noted somewhere in their description or somewhere in the class page.
==Using Items==
Using items in most cases does not require a roll. In unusual circumstances or unfavorable ones (e.g. trying to start a fire with damp wood), you may be required to roll to see if your item use goes as planned.
==Saves==
Your saves (Fortitude, Reflex, and Will) are what you roll in order to avoid disfavorable effects, such as rolling a Reflex save to avoid a trap or a Will save to resist the effects of a spell. The DM will tell you what to roll if the situation calls for a save.
When you roll a save, you use the entire value listed on your character sheet, not just the base save value derived from your class.
Category:Game Mechanics