GDebi will automatically propose the installation of dependencies in versions
that are available in Trisquel's repository. For missing dependencies or
dependencies in newer versions than those in Trisquel's repository, GDebi
will report them. You can download them from the same repository you took
the .deb from, so that you know their versions will be matching the one the
program expects. You may have to do the same for those dependencies, and so
on.
But, again, upgrading a package already installed on your system may create
problem for some some of the already installed software that depends on it
and may be incompatible with a newer version of the dependency. In
particular, you do not want to update fundamental libraries such as "libc6".
That is the work of the distributions to build and put together a set of
packages that are compatible with each other. To a varying extent,
administrators of PPAs you add (that you must trust, as SuperTramp83 points
out) do that same work to make possible the installation of a few packages on
a given version of a distribution. Upgrading a package in another way may
create incompatibilities. And PPAs may conflict between each other.
Also, you probably do not want "to take some linux classes". You want
GNU/Linux classes: https://www.gnu.org/gnu/linux-and-gnu.html
