You can't really synthesise footsteps or gun reload effects. You need to record them happening. One of the best ways to get sound effects is through foley. A foley artist is someone hired by the film studios to dub over sound effects using every day objects.
Bones Cracking = Breaking a Cabbage
Shotgun loading = Putting batteries in a torch
Get yourself Cool Edit 2000 - it's shareware ....
Can I ask you a Question?
What is it?
It's an interrogative form of sentence, used to test knowledge. But that's not important right now.