Put a little anti-seize on the threads on the hub.
Match the splines on the hub to the splines on the inside of the freehub body.
Push the tubular bolt into the freehub body and turn it clockwise with a 10mm hexagonal key.
Tighten the bolt to lock it.
Repack freehub body with new balls
Pack the races in the freehub body with new grease and place new balls - of exactly the same size as the old balls - into the grease. Using new balls prolongs the life of the other parts. Use the same number of balls that came out. If you're not sure how many, or if you suspect that the freehub body was packed with the wrong number of balls, fill each race with balls then take one out. The balls need some room to roll.
Assemble the other side and adjust the hub.
The cup on the drive side is part of the freehub body but you can deal with it in the same way you would treat a cup in a hub shell.