An acrobat, sometimes called an aerialist, is someone who does activities like juggling, tumbling, tightrope-walking and other gymnastics. Today, acrobats are usually seen at a circus. Before television, travelling acrobats would visit towns and castles to perform for the people's entertainment.
An actor is someone who plays pretend for a living. Actors put on plays on stage, or are in movies or television shows pretending to be someone else or someone made up. Their job is to entertain people. Sometimes a female actor is called an actress.
Applauding is clapping after something happens to show you like it. People in an audience applaud after a performance like an opera if they think it was very good.
Applause is clapping of hands to show appreciation. Applause happens when a group of people in an audience all applaud at once.
An audience is a group of people that are watching some kind of public event, like a concert or a speech. The people organizing the event usually hold it somewhere there are a lot of chairs, so the people in the audience can sit down while they are watching.
Ballet is a special kind of dance that was originally from France. Ballet has a lot of technical movements with their own names, like pirouette and battement. Ballet is usually danced to classical music.
You perform something when you do it so other people can watch you. Most performances are done on a stage and watched by an audience.