I needed to back up some files right away and my friend used her portable hard drive to do it for me. Can I transfer them safely from her portable hard drive onto one I buy and if I can do that will that delete them from her hard drive unit?

If you use the "cut" and paste method of transferring the files it will remove them from her external hard drive. I have an external hard drive that I use to store my downloaded movies onto when I run out of room on my regular computer's hard drive. I can move the files back and forth all I want and when I remove them from the external drive they are gone forever from the external drive.

twinkiedooter- can ypu please explain how I do this exactly step by step.. just want to get it right...
She had plugged her external hard drive into the front of my computer there is only one slot there, do I plug the one I buy into another slot in the back then and just cut and past each file
Appreciate it just not sure.

If you use one of those little flash drives, it works just the same as though it were an internal drive. Is that what you are referring to?