Deglazing a pan is one of those kitchen techniques that sounds easy enough that many of us trick ourselves into thinking we know how to do it when we actually don't. I didn't really know until I went to culinary school.
After sautéing or roasting a piece of meat in a pan, remove it and pour off any extra fat (as in the case of roasting something large in the oven). There will be little bits of food stuck to the bottom; usually quite cooked. These are the caramelized droppings from the juices of the meat. These little bits are packed with flavor, and only need a liquid, such as wine, stock, or juice to release their flavors.
Pour in a few tablespoons or so (enough to cover the bottom of the pan 1/4" or less), with the heat still under the pan, and scrape the bottom with a wooden spatula vigorously as the liquid comes to a boil. Do not let it boil for more than a few seconds and you make sure you've released all the particles from the pan. You have deglazed the pan and can now use the resulting liquid to make a sauce or gravy.