Improvisational comedy is a form of live theatre in which a performance is created in the moment, with players creating the characters, dialogue and action as they go.
A popular art-form in its own right, improvisation is also an important tool for writers, comedians and pretty much everybody. The requirement for building ideas with others requires keen listening skills, collaboration and creativity. Improvisers around the world have developed principles through shared experience which make those skills easier to learn and apply. 
You don't need any experience to learn the skills of improv, and everyone has experiences, a point of view, and a creative flair to bring to the class and stage.