$ cd ..
( Is shorthand for go back one step in the directory tree )
$ cd ~
( Is for /home/coolguy, if you got more then one user ~coolguy1 or ~coolguy2 )
$ cd ~/Downloads/Backgrounds
( Is for /home/coolguy/Downloads/Backgrounds )
For really fast typing don't forget the tab-key for autocompletion:
$ cd ~/D "tab-key" /B "tab-key"