|Acting is a big industry. There are actors everywhere from the theatre to films, from TV to radio, and even on the street in the form of mime. Yet acting is not easy - in fact, like playing music, it is almost impossible to master.
To be a good actor, you have to be able to get inside a character and literally live as them - to convince your audience, and, for a moment, even yourself, that the character is who you are. Given that all you will probably have to work with is a few written words, perhaps costumes and a set, and your imagination, it's a difficult undertaking.
The range of skills that an actor must have to be effective is very wide. You need to have a mastery of your body for movement that can include fighting, dancing, or evocative expressions. Your voice, too, must be clear enough to be understood from a distance, and you might also need some talent in singing or putting on accents. The most difficult aspect by far, though, is the emotional one, as you must be able to assume different emotions at will - crying on demand, for example, or being able to give an effective illusion of happiness or excitement.
One of the most widely-used means of portraying realistic emotions is Stanislavski's theory of method acting, which you would do well to study if you wish to become an actor. Basically, the idea is that when you are acting, you think of a time when you felt the emotion you wish to portray. For example, if your character is sad over the death of their mother, you might think of the time when you were small and your dog died, and so start crying. There's more to it than that, but that's the basic theory, and it can give a very convincing performance when done correctly.