In the meantime, if you're using the full editor with those buttons above the text area, you should also see a column to the right of the editing area that has a table of smilies, followed by a list of board settings. The first one is BBCode, and that's a live link. Click on it (or better yet, right click and open in a new tab, or whatever works for your browser) to get a long page filled with examples.
The specific answer for URL is that the target link goes inside the first set of brackets so that it might read {url=http://example.com}Example link{/url}, where I've used curly braces instead of brackets (because [noparse] doesn't seem to work; I guess phpBB is using a different version of BBcode than vBulletin).