For a single document, just use File>Export and choose EPUB from the pop-up labelled Format at the bottom of the Save dialogue. (That's what it's labelled on a Mac, may be slightly different if you're on Windows.) If you have a book, there's an Export Book to EPUB... command on the fly-out menu on the Book panel.
Crashes InDesign every time when I try it lately. That's probably just me, but don't say you weren't warned.