The Kobo manual explains how to add fonts. It is very easy. You add a folder called fonts in your root directory and then copy the fonts you want into that folder. You will want to chose fonts that have four variants so you get the normal font, bold, bold italics and normal italics.
These is a video here: http://www.youtube.com/watch?v=KU7JpaKlyMc
I have not watched it. The link to all the Kobo user guides can be found at: http://www.kobo.com/userguides
I'm not a huge fan of using the store, so I just don't click on the buttons that take me there.