A "patch" in Google/Facebook/Twitter is the same as a commit. It has a (mostly) descriptive commit message, references to bug tickets and might contain links to documentation, screenshots and mocks.

You basically work on a "patch" (changelist), get feedback from others and send it out to review at the end. Before you can submit (commit) it, you'll have to sync to "head" (to have the latest changes) and run all tests. ^ most of this happens automatically, and as most changelists ("patches") are small, this happens very fast and async in the background.