SandM

You schedule the appointment from the USCIS website you just find the local office in their website menu and schedule it there. They don't need the letter just your DL and GC. This is it:)

There is a N-400 guide on this website and as far as getting a stamp you need to make in InfoPass appointment at your local office and they will stamp it, you can schedule the appt online
This is the link for the guide:
http://www.visajourney.com/content/naturalization_guide