I'm assuming you don't have a mod chip, or any prior knowledge of modding.
First, to do anything with your Xbox, you'll need to install a modchip. Before you buy one, make sure it is compatible with your Xbox version. If you're unsure about which version you have, go to
http://www.xbox-scene.com and click on XB VERSION on the top left of the page. After you get your modchip, find a guide on installing it on Xbox-Scene. After it's installed correctly, you'll need to make an EvoX(or other dashboard of your choice) boot disk. For this you'll need a writable media type that your Xbox can read (DVD+-R/RW is the best, but some will read CD-RW. don't bother with CD-R, almost no Xbox can read them), a disc burning program (I'd suggest Nero), and an ISO of the Auto-installer for your dashboard(I will not tell you how to obtain this, it took half a year before I figured out how to FTP, which come next), and also a dummy file(search on Xbox-Scene). Burn the ISO and dummy file to your disc, and then put it in your Xbox. Hopefully it will read and you'll be able to install your dashboard. After all of this, you'll need to FTP to your Xbox to be able to transfer any files. Download FlashFXP and install (if the trial runs out, don't worry, uninstall and reinstall and your good for another 30 days), then connect your Xbox to your Router/Ethernet hub, then turn on your Xbox. Next, you'll need to find out your Xbox's IP address, which by EvoX default should be 192.168.100.10, but check under the setting menu just in case. Open FlashFXP, and go to Quick Connect. For IP/Address, put in your Xbox's IP address, and for name and password, put in "xbox" all lowercase without the quotes. Then click connect, if it doesn't work, you might have to change your IP address in Network Connections by going to the properties menu of your Internet connection, going to TCP/IP settings, and changing it to the same as your Xbox's except for the last digit which MUST be different. After you connect to your Xbox, you'll be able to see C,D,E,F,G,X,Y,and Z drives. F and G won't be usable at first, you'll need to "unlock" the full stock drive to use F and you can't use G: unless you have a HDD larger than 137 GB. C is the directory where the system files are located, D is the DVD drive, E is the main data storage drive, and X,Y,and Z are cache folders only created after playing a game which uses them for additional temporary storage. I hope this helped, because it took me a fuckload of time to type out, and if it didn't, GO TO XBOX SCENE. whew....