The best place to get practice using Confluence is in your own personal space. Every registered Confluence user can have a personal space; to set it up, all you have to do is log in and click your name, which appears as a link at the top of the page, next to the word "Welcome." You'll be prompted to set up your space.
In your space you can add, edit, and delete pages to your heart's content. By default, your personal space is viewable by other Confluence users, but you can change the permissions in your space by clicking "Browse Space" and going to "Space Admin."
By the way, your personal space is a great place to organize projects you're working on. You can create a page for the rough draft of an essay, or different pages for different parts of a draft; another page for a bibliography; and a third for related websites. You can create a separate page for notes on each book and article you read. If you use the labels feature of Confluence, you can search the contents of your personal space quickly for particular kinds of information.