When I got started with my pressure cooker I started small. Easy.
Mashed potatoes is incredibly easy. Put the potatoes on the rack with the water level below the rack.
Cook for 8 minutes at 15lb pressure, then mash.
Dry beans are perfect for the pressure cooker. You'll have to do a little experimenting with cooking times though. I like lima beans, and cook them from dry in 12 minutes at 15lb pressure.
Stock is another easy job. Put a few pounds of bones and meat scraps, or a chicken or turkey carcass, a couple roughly cut onions, a few carrots and celery stalks in the cooker. Add whatever herbs and spices you want, I like Sage and Coriander, and cook for 90 minutes at 15lb.
If you want to store it for later use, turn it into a glace. Put the stock in a wide pot, and simmer until concentrated. You will end up with a piece of stock that resembles a very stiff jello. Freeze it, and add to any recipe you want. It will be very concentrated, so start with just a little at a time.
I also suggest not putting any salt in to start with, it can get over salted pretty quickly.
Any meat goes great in the pressure cooker.
Say you have a few people coming over for dinner, and you forgot to defrost your roast. Put it in the pressure cooker straight from the freezer. Add an inch or so of water, and some herbs and spices. After it comes up to pressure, cook for 20 minutes or so. Then you can finish it in the oven for another 20-30 minutes.
Meat won't brown in the pressure cooker.
Custard is an easy dessert for the pressure cooker. Mix up your custard, put it in custard cups on the rack in the cooker. Add water below the cups, and cook. You'll have to experiment with the time, but 15 minutes is a good start.
The pressure cooker is by far my favorite cooking tool. I have a 6 quart and a 4 quart one, and I frequently use both at the same time.