It's not *that* hard...
Presently, there are few pre-packaged installs, so the recommended method for most users is to follow these instructions. Even if you have a package system that includes IMFavorites, you may wish to manually install for a variety of reasons. A likely reason is simply that the latest version of IMFavorites may not have been packaged.
So...
First, you need to download a IMFavorites release. Newer is generally better, but unless you know what you're doing, you should use a release marked "Stable." So download the newest Stable release that you can. (On the other hand, if you discover a bug and want to report it, it is helpful to try to run the "current" IMFavorites, as we have been known to fix some bugs before they are reported.)
Copy the tarball you downloaded into a temporary directory. Untar it as follows:
tar -zvxf imfavorites-1.X.X.tar.gz
cd imfavorites-1.X.X
./configure
Once that completes, it's time to build and install IMFavorites (Note that you will have to be the superuser to make install).
This is as simple as:
make all make install