Mine (a Vax) is small but perfectly formed and doesn't need putting together to use it, so it is ready a few seconds after you decide the floor needs a wash. It sits with the vacuum waiting. The water container only needs refilling occasionally.
When you press the lever in the handle, a little water goes from the container past the heater and out at the other end through the mophead as steam. You push the mop backwards and forwards a bit to wash the floor, either adding more steam or just mopping.
There is no extra water left on the floor - only enough goes through to dampen the mop and so the floor. The floor is a bit damp, but a lot less than using a conventional mop. It dries in a couple of minutes, completely.
I bought a refurbished one - unused but returned because of cosmetic faults or because the buyer had changed their mind, completely overhauled and with a year's guarantee. I can't find what the fault (if any) was with mine. It was far cheaper than new.