Install it (or activate it) using a font manager or into the font folder for your OS.
not to sound dumb, but how would I activate them?
If you are using a font manager, it will either have an activate or install option in it. The help file for the particular font manager likely has the process written down.
If you are not using a font manager, then depending upon your OS, you simply install them. I am using Windows and so installing a font is as easy as right-clicking on the font file and choosing install. I have no idea how to installa font on a Mac if that's what you are using. Either OS font installation can easily be Googled, though, if you are not sure.