Command to erase a file permanently
I'm not sure how confident you're going to be using Terminal commands as a brand new user, so I wouldn't recommend doing anything that can permanently, no questions asked, delete data from your hard drive. 

It would be far safer to delete files to the Trash using the standard Finder command
 Cmd ⌘   Backspace ←  . 

Then when you are happy you really didn't need the files, again from the Finder
 Cmd ⌘   Shift ⇧    Backspace ←    will empty the trash.

That in itself wouldn't securely erase, preventing all recovery efforts; but from a standard user perspective, they would be gone &amp; the hard disk space freed up to be used again.