A .tar file is little more than a concatenation of files into one single file
(plus where to "cut" to get the individual files back, plus their metadata
such as their names, permissions, etc.). The .tar archive is usually
compressed, i.e., you have a .tar.gz or a .tar.xz or...
And you need not use the terminal to deal with .tar archives (compressed or
not). You can use "File Roller", GNOME's archive manager, which is installed
by default and integrated into the default file manager. For instance you can
select some files, right click on them and choose "Compress...". Or you can
right-click on an archive and choose "Extract here". By double-clicking on
the archive you get more options (e.g., to add files to the archive or to
extract individual files).
More generally, with Trisquel, all basic (and not so basic) things can be
done without the terminal if you wish. That said, taking the time to learn
the use of a terminal (and of the most basic commands) will save you a lot of
time for the rest of your life.
