you probally want to use the terminal, because if you don't learn how to do it that way and your fix doesn't work, then your really going to be up the creek
I suggest using nano to edit the file, becuase its easy to use.
cp xorg.conf xorg.conf.backup
now find the part of the file you want to change, and change it
then save by hitting control+x and then answering Y to the prompt
Reboot or restart X
Now if you find that you fried your mouse completley because you edited the file incorrectly, you can fix it like this:
cp xorg.conf.backup xorg.conf
restart X or reboot
If you find that you TOTALLY killed X and cant even get it to load, flip over to a virtual console by hitting control+alt+f2, log in, and edit copy the backup that way.
Good luck, and I hope you enjoy learning linux
If you dont give up within 6 months, you'll probally NEVER want to use windows again