If you are interested in books or "tracts" on becoming Catholic, I would suggest you first read Pillar of Fire, Pillar of Truth. You can read it online at Catholic Answers or you can order a copy. It is a very good introduction to the Catholic Church.
If you are curious what Catholics believe, I would suggest the Compendium to the Catechism. You can read it online or buy a copy. (It's probably better to buy than try reading online, but that's just my opinion.)
Finally, this brief web page describes How to Become a Catholic.