You go into our utilities section and select Special Debuggers category and the system and press search. Download it. Load your rom. Press the debug key. The assembly will be output to a text file. Read some documents on assembly. How about this one that deals specifically with hacking compression in nes roms.

http://www.romhacking.net/docs/fceud_tutor3.txt

This is my last response. I'm not trying to be mean here but you learn from reading on your own. There is no sense in me doing another tutorial in this thread when we have plenty in the database already. Even if you don't understand them, just keep reading the docs. The stuff will unfold as you go.