I have both white and black truffle oil that I use as a finishing oil. But, I have also used it in cooking, where it is encapsulate so as to keep it's wonderful aroma and flavor from evaporating into the air, such as in ravioli, or in a filled pastry shell. It has a pronounced flavor that can overwhelm other flavors if used in excess. But that is true of so many good things, such as many fish sauces, herbs, and spices. Think of it as a mushroom flavored seasoning.
You can also purchase truffle salt, which has that same great flavor. It's made by adding pulverized, dried truffle to kosher, or sea salt. Like the oil, you don't generally cook with it, but use it as a finishing salt. I love both varieties. They are so good.
Like most strong flavored foods, you either love it, or strongly dislike it. Most people that I've met like it. DW doesn't much care for it, unless it's hidden in something so that she only gets the mildest hint that it's in there.
As for how to use it, after making duxelles, and before stuffing into, or topping it onto whatever, add a few drops of truffle oil to the mixture, then proceed as normal. Or, add a quarter-teaspoon to your gravy, after you remove it from the heat. Another great application is to mix it with butter for use with mashed potatoes. You can drizzle a bit onto a steak, at the table. You can put a touch of it into your Italian vinaigrette dressing for salads. It's great drizzled onto savory baked chicken too. Add a bit to your homemade chicken soup, again just when you serve the soup. I love to add it to creamy soups, especially cream of mushroom soup, homemade of course. It's great added to a veloute, or bechemel sauce, and with egg dishes. In the end, you just have to try it with different foods, and let your taste be your guide.
Enjoy your truffle oil. It really is great stuff.
Seeeeeeeya; Chief Longwind of the North