There's a difference between the relay coil and the relay contacts — which is the whole point.
You can buy relays with almost any coil voltage between 5V and 240V (or more) either AC or DC. These relays are available with gold-plated contacts rated for a few milliamps to huge copper buttons rated for hundreds of amps.
There is a structural difference between AC and DC relays, but I don't think there's a difference in how you use them. Just buy the correct relay for your task and the tutorial should apply.