0 to say who you are when you arrive at a hotel so that you can be given a key for your room:
1 to go to a desk at an airport, port, etc., or a hotel and say that you have arrived:
2 to use the internet to check in for a flight:
You will find it most convenient to check in online.
We then checked into the hotel for a weekend of unashamed luxury.
After driving all day, I was so pleased just to check into a motel and relax.
The police wanted to know whether any new guests checked in on Sunday evening.