You should not be in the habit of downloading and installing programmes
from outside of the repositories unless:

a) you know what you are doing
b) you do don't care about messing up your installation
c) you don't expect others to bail you out afterwards

The best and the only way, to my way of thinking, for newbies to install
software is to use the package manager or download deb files that are
specifically made for your version. Otherwise you risk not being able to remove
it properly later and will have to live with the results.

Any idiot can post a file to the internet and any idiot can download and install
it. However, there are no guarantee that the file will work and won't mess you
up royally. People go to a lot of trouble to put packages in repositories and
can guarantee their authenticity. There are between 24 and 35000 packages in the
repos. There is very little that you might need that is not available. On top of
this you have other resources at your disposal such as getdeb.net.

There is something to be said for learning how to compile from source code, but
you should not do this on your main computer.

People can tell you how to do anything, but whether you should be following
their advice is another story.

My advice is to stick to the repositories found in Synaptic until you understand
more about how Linux works and why things are the way they are.