But if you get rid of terminal then you're left with the package manager.
How do you go about installing things other than what's available in the package manager?
apt-get is a package manager for the terminal. You can also use a gui front end like synaptic(which I generally use), or software center(ubuntus's default, and what my mother uses). There's also aptitude for the terminal which is recommended over apt-get, but I've never gotten on with it.
Installing software outside the repos should be the last choice, but most if they're packaged at all will have a .deb available(assuming debian based distros here(.rpm for the other big ones)), and you can use the gui gdebi to install it.
Otherwise, you can compile from source, but that requires the terminal of course. Outside the purview of the n00b, but not hard, and it's nice having the option.
Oh, and there's a few windows-like packages being worked on that package everything together with statically linked dependencies, but I wouldn't like running my system that way. You end up with bloat having multiple package versions installed. I prefer the standard model.