A budget is simply a way of saying "I don't want to spend more than this much, on these kinds of things, during this time." You choose an amount, a time period, and which accounts and categories should count toward it — only actual spending counts, never income or money you move between your own accounts. You can set up a one-off budget for a single stretch of time, or a recurring one that automatically starts a fresh period once the last one wraps up.
Once it's set up, you don't need to do anything else — every matching expense you record gets counted toward it automatically, and you'll get a heads-up if you start getting close to (or go over) your limit.