In SD, how to get address etc. for a commercial Partner via ADDNR

Hello all,

I am new to SD (and new to ABAP for that matter) so have a lot to learn. I am to write a report program to produce a list of documents containing information about commercial partners and their full address. That is to say, town, country, postal code etc... Now here is a question in three parts:

1) Where and in what table do I find address information about a commercial partner (SD module)?

2) Is there a standard function module where I can supply it with the address number and get all the address and perhaps some other info in return?

3) I tried to understand the standard SAP program (i.e. FFP2) as to how it gets the partner address and other info. But very quickly I got lost in transfers between includes, programs, screens, sub screens, function calls, etc... The program seems to read the data from some mysterious table INTO a structure and then display it on the screen. Now, for future references, how do you figure out the source of information for a screen field when the field it is mapped onto a structure and not a real table?

Your help is greatly appreciated