Levelling Guide

== At a Glance ==
As you go on adventures and overcome challenges, you will gain experience. When you've completed enough experience, determined by games played, you will gain a level.
When gaining a level a class often grants additional features, as detailed in the class description table. Some of these features allow you to increase ability scores, either increasing two scores by 1 or by increasing one score by 2. You can't increase an ability score above 20. In addition, every character's proficiency bonus increases at certain levels.
Each time you gain a level, you gain 1 additional Hit Dice (some races get more). Roll that Hit Die, add your Constitution modifier to the roll, and add the total to your hit point maximum. 
When your constitution modifier increases by 1, your hit point maximum increases by 1 for each level you have attained. 
==== Tiers of Play ====
In the first tier (1-4) characters are apprentice adventurers. They are learning the features that define them as members of particular classes, including the major choices that flavour their class features as they advance. The threats they face are relatively minor and usually pose a danger to a local farmstead or village.
In the second tier (5-10), characters have reached a level of power that sets them high above the ordinary populace and makes them special even among adventurers. Many spell casters gain access to 3rd-level spells at the start of this tier, crossing a new threshold of magical power. Many weapon-using classes gain the ability to make multiple attacks in one round at this tier as well. These characters have become important, facing dangers that threaten cities and kingdoms.
In the third tier (11-16) characters have reached a level of power that sets them high above the ordinary populace and makes them special amongst adventurers. At the 11th level, many spell casters gain access to 6th-level spells, some of which create effects previously impossible for characters to achieve. Melee adventurers may also gain features that allow them to make more attacks and do impressive things with them. These mighty adventurers often confront threats to whole regions and provinces.
At the four tier (17-20) characters achieve the pinnacle of their class features, becoming heroic (or villainous) archetypes in their own right. They begin to confront threats against continents (and the world) as they reach a level of legendary status that some regard as demigods in myths.