Ramp builds a ramp from the base of the engrave to the edge of the stamp face. It’s useful when you have fine detail that would be ‘wobbly’ if unsupported by a ramp.
1 or 2 pass depends on your machine and it’s capabilities. I do 1-pass, but I doubt our machines are the same.
If you’d used the search function of the forum, there’s a lot of info you will find: Ramp mode for rubber stamps