Yes, that's all there is to it. Sign up once, get your barcode, take it to any of the parkruns, any Saturday, and your results will all be stored on your home page. There isn't really any check in at the start either, although there is generally a briefing, where they'll ask if anyone's a first-timer, and point out anything you need to know about the course. And parkrunners are generally a friendly bunch, so if you have any questions when you get there, just ask.