When you adjust coilovers do they all have to be on the same height?

Ksport Kontrol Pro Coilover system
Honda Civic

Added (1). A guy is selling a car, but it's like way too low. He said you can adjust the coilovers and I was watching a video, it seems easy but takes some time, even for just adjusting one. Do I have to get behind all four wheels and adjust them the same?

Yes, you have to adjust them all. Adjusting one does not adjust all of the others.