Easy and simple:
- use cp
cp /home/yourfolder/afile.ext /mnt/usb/afile.ext
this will create a copy in the folder /mnt/usb, however, as this is the mount folder TO
the usb stick, the file will in effect be created on the stick. Provided the USB drive is inserted/mounted, but you know this...
- use the file manager
just enter the stick, see it apear and open TWO file managers. Drag and drop from the one to the other. One "points" to the usb stick, the other to the folders containing the files to be backed up
- use rsync
a very flexible little tool that has to be part of anyone's tool chest, check out the manual
Placing files back is just as easy: just put the file back from the back up to the required spot. In fact, it's not even a silly idea to have a regular "snapshot" of your whole home folder
to an external harddrive...
Everything you do and register ends up in your home folder (wow, sounds like that "warning" in Tron, where a program gets its disk - only the deleting is not there, dont worry) - so it's a sane move to back up the whole thing