Just like a weight lifter has to go to the gym to work on his skills and keep them up, an actor has to do theater to work on his skills and keep them up. If you don't want to start on stage right away, acting classes are available. Most schools have some type of drama class that is available. These are also great places to start. They teach the basics as specified above but in a different atmosphere.
Acting classes are very specific in what they teach also.
Instead of teaching you everything on stage at once, an acting class takes one section of theater and breaks it down into smaller parts so you learn more. Acting classes are great places to start for those who suffer from stage fright. They teach you how to eleviate you fright and be comfortable on stage in front of crowds under the lights. I have experience in acting and need to get a headshot. Headshot are in my opinion one of the most important parts to an acting career.