Tang, you don't know what you've asked
I take it you're new to subsimming? That is a
very deep question you pose, "what exactly do you do from sighting to sinking"!
Here is a site that may provide some useful info:
http://www.communitymanuals.com/shii...itle=Main_Page
This is the SH3 Wiki, and while it's oriented towards SH3, the basic principles are the same whether you're driving a u-boat or a fleet boat.
I'll leave it to you to dig out the useful stuff, but be assured there is plenty in there that will help you!
Good hunting!
DH