holding it in. The hardest part is lining it up properly so it operates smoothly and tightening the screws up.
A handle may have an extra screw at the bottom and the dead bolt may have 2-3 more pieces but the concept is the same.
If you have some extravagant mortised style action it may or may not be anymore complicated, but the brand name of the action will be written on the hardware so you can google it and youtube how to reassemble it.
Don't give up. Keep at it.