When you arrive for a shift you check in at the volunteer tent. It takes a few seconds.
Your badge
Your account has a badge with a QR code on it. Open it on your phone before you get to the tent — signal at a festival site is unreliable and the page is easier to load in the car park than in the queue. A screenshot works just as well; the code does not change.
If you have no phone or no screenshot, give your name. Whoever is on the tablet can find you by name or email in a second.
At the tent
Somebody scans the code or types your name, and you are checked in. The tablet shows your name, your crew and your shift, so if it shows somebody else's you both know immediately.
Check out at the end if the organization asks you to. Some do and some do not; they will tell you.
When the wifi is down
The tablet keeps working. It holds the day's roster and records check-ins on the device, then sends them up when the connection comes back. You will not be asked to wait, and nothing is lost — the tablet catches up on its own, without checking anybody in twice.
Your hours
Checking in and out is where hours come from for most organizations. See Your hours for how that is counted and what to do if a shift is missing.