Which linux distro do you have running?

You should be able to open the terminal using CTRL+ALT+t or CTRL+ALT+F1.

basic commands:

cd [some place] = go to
for example, Go back to the topmost location by typing cd ~

In Ubuntu linux, you can find the usb drive by typing cd ../../ and then hitting TAB to give a list to show where you can go next. I think USB would be in a place called /media

You're going to have to read up on this but it's more simpler than DOS. That's what I think.