There are many tutorials available online, but the one that I referred to most often was on the "hostess with the mostess blog".
The process is very simple. I cleaned the tiles and cut out some squares from souvenir travel maps. (A good way to make use of my travel souvenirs--and I get to see them each day instead having them unseen in a bin somewhere.) Then I applied layers of Mod Podge, letting it dry between layers. Finally, I applied a layer of clear finish on top as a extra layer of protection. For the back, I glued some cork sheet to protect the table surface from scratches from the tile. That's all! Can't wait to put them to use with some coffee cups.