Anna-Maria; Gravies differ from sauces in that they are flavored primarily with meat juices, extracted either during the meat preperation, or through simmering on a low boil for an extended period of time.
Various thickeners range from starches such as cornstarch, tapioca, and arrowroot, to white flour, to silken tofu. Here are some basics.
Flour based starches are made from pan drippings, demiglaze, broths, or stocks. When pan drippings are used, the pan is usually deglazed with water or wine after the meat is removed. Just add a cup or so of the lizuid to the still-hot pan, and stir the liquid while scraping the pan bottom to dislodge and dissolve the browned bits. This is what flavors the gravy.
There are two ways to thiken this liquid into a proper gravy. The first is to make a thin paste with flour and water, and then add a few tablespoons of the hot broth to the paste, to temper it. Then slowly pour the flour slurry into the simmering liquid while whisking vigorously. Let the gravy cook for three or four minutes and test the consistancy. If too thin, make more slurry and repeat the process. Season to taste with salt, pepper, garlic, etc.
The second is to make a roux by mixing equal parts butter and flour in a pan, and heating while stiring until a paste is formed. When the roux is formed, add a cup of the flavored meat broth, stirring vigorously to ensure a smooth gravy. Add more broth until you reach the proper consistancy. Correct the seasoning to taste.
Starch gravies have more of the natural meat flavor as they add now flavor of their own. The gravy will be more clear, translucent. To make a starch-thickened gravy, make a slurry of equal parts water, or milk, and starch (corn starch, arrow root, tapioca starch). Bring the flavored liquid to a rapid boil and slowly drizzle in the slurry, sturring with a spoon. Let boil for one minute and test the consistancy. Add more slurry as required. Correct the seasoning.
Remember, the added liquid from the slurry, and the additional flavor added by the flour or starch, will dilute the broth flavor. So you have to make sure the broth, stock, or pan drippings have strong, almost overpowering flavor so that it can be diluted to great flavor as it's made into gravy.
As you experiment, you will develop an intuitive ability to gauge the correct amount of salt, pepper, thyme, etc. to get the taste you want. As far as consistancy goes, the gravy should coat a spoon, but not encase it.
Hope this helps.
Seeeeeeya; Goodweed of the North