Oh boy... You should be asking your "friend" who sold you this modded box.
To connect to your Xbox, all you really need is a CROSSOVER Cat5 RJ-45 network cable. You CANNOT use a standard straight thru cable unless you have a Hub or Router.
If you want to connect your box directly to your computer without any other hardware, you need the Crossover. Recommended software to FTP is FlashFXP. And if you have Zone Alarm or any other firewall software installed on your PC, turn it OFF before attempting a connection or transfer.
I would suggest you install BoxPlorer on your Xbox. That way you won't need to FTP to the unit just to delete files.
OK? This is it, that's all you need to know. Everything else on "how to" is in the FAQs and Tutorials. If you don't understand the documents during the first reading, go back and read them over slowly 3 times. You will get it.