I pretty much agree with Uncle Vic. As clarification, you can use oil/butter just as you would to saute something in preparation for stewing (maybe this varies with manufacturer?), but don’t fill the cooker with oil unless it’s a pressure fryer. The basic issue, I understand, is that frying-temperature oil can melt some gaskets resulting in "ka-boom!" A water-based pressure steam gets hotter than 212 F, but not that hot.
Also, if the cooker’s aluminum, you won’t want to cook high-acid stuff (like tomato sauce) in it, just as in any other aluminum pot. And some manufacturers discourage cooking beans, as occasionally a skin flies into the steam valve and clogs it (I’ve never had a problem with my T-Fal).
Haven’t been using mine a lot lately, but in general it will cook anything you’d normally stew. Generally you want to use LESS liquid than you normally would (although you need some to keep food from burning and some manufacturers specify a minimum amount of water), as there is virtually no loss of steam, and pressure cooking tends to extract more juice from many items (similar in result to a crock pot).
Other rule I learned is that with beef, you always must let the pressure drop naturally (rather than running water over the cooker or using a quick-release valve). For some reason, beef toughens from the rapid change in temperature while other meats do not.
Lorna Sass’s "Cooking Under Pressure" has a pretty good selection of recipes. It includes pressure cooker risotto, which is the only reliable method I know of to make good risotto without constant stirring. Some of the recipes on those websites look interesting. I know the first thing I cooked in mine was a beef stew.