You will want to read the information at http://www.oilpulling.com,
as Mikey suggested, for basic information and background. That site also contains the basic OP protocol (1x per day before eating, for 20 minutes, using sesame or sunflower oil). My personal suggestion to those beginning is to do that for a couple of weeks to see what benefits or detox reactions you experience. Because we all bring very different bodies to the process, there is no way to predict what reaction this or that person will have to all the different oils out there to use, but the standard protocol at least has a "history" with it as Dr. Karach outlines at oilpulling.com.
There are many, many reports of improvement with various dental/gum issues, bad breath elimination, and the like. You should read through the "R" and "RN" posts at the top of the forum page to learn about experiences that OP'ers have had or for accounts of results you may be looking for. You can try all sorts of different oils, although it is the consensus here to avoid oils that are not good for health in general like soy, canola, peanut, vegetable, corn and other highly processed "industrial" oils.
I have used sunflower, safflower, sesame, olive, walnut, grapeseed, coconut, flax, and probably a few others. For a while I added some oregano oil to whatever oil I was using. (Which elicited a huge sore on the bottom of my tongue that was completely horrible and which I hope never happens again!) I have tried to stick with the least-processed and organic oils, but that doesn't always happen!
This is a great therapy and a good place to begin at Curezone. Also, this forum seems to attract the nicest people at Curezone (if I do say so myself!)...