A jointer makes a board flat, it can also true the edges for glue up, cut rabbit joints, cut tapers and curves as well.
A planer makes both sides parallel and reduces the thickness of wood.
Maybe you don't for flooring if the boards are relatively flat and you have a good blade. My initial woodworking training included a jointer and I am convinced that I must have one, although I have been getting by with hand planes.
The sequence I was taught is this: 1. flatten one face on the jointer 2. true one edge on the jointer, you can rough it out with a TS, cut opposite side parallel with TS, then joint to width 3. use planer to make sides parallel and get within a hair of final thickness 4. tool the wood 5. sand/scrape (I usually use 60-80-120) 6. assemble 7. final sand/scrape (150-220)
I've probably left something out, but I'm sure someone will remind me. You can substitute hand planes during steps 1-3, it's just more labor intensive.