How is The Importance of Being Earnest a "comedy of manners"? Is this play actually funny? What is Wilde satirizing?

I think this play is actually funny but only sometimes. If you really understand whats going on it will be funny for you. But some parts that are suppose to be funny, really don't make me laugh. This is a piece of literature for the Victorian era which is based on realism and not romanticism. So it tries to focus more on whats happening everyday.