To do nitrous, we usually let the can sit nozzle up for awhile to let the cream settle. From here, there are two ways you can go about it.

1) Put the nozzle in your mouth, and tip the nozzle very slightly until you hear the gas come out. It'll be loud. If cream comes out, you're tipping it too far.
2) Do the same, but like NightProwler said, empty it into a balloon. If it's in a balloon, you can breathe the n2o in, then out into the balloon over and over again 'til you feel it, or you can hold the gas in your lungs for as long as possible.

Nitrous, like marijuana, has a reverse-tolerance effect meaning your first couple times may not be very intense. I felt it my first time, but it was nothing compared to the rush you get once you're more experienced. For my first time, I got a tingly/numbing sensation, and a short buzz.

Enjoy. Nitrous is a LOTTTT more pleasurable than you'd ever imagine.