First off, I don't measure. I cook by sight and feel. I know this is a problem for many who ask for recipes.
There are other cooked gravies from fat/oil drippings and flour but those can cause a headache for the beginner. This cornstarch gravy is easiest. If you cook down a really rich broth your gravy will be good. If you only whip up a thin clear broth or use store canned broth you won't get much flavor for the gravy.
I use a good rich broth either from the chicken or turkey. If I have stock from my freezer I cook the giblets in stock making it richer.
If I don't have stock I cook the giblets* with celery, onion, carrot, garlic, salt and pepper with a little butter and make a rich stock. Cook it long and slow, add water if you let it cook away too fast.
Also boil an egg or two.
Once youhave a good stock base strain everything out of the broth so that your broth is clear. You should have about 4 - 6 cups.
Finely chop the gizzard, liver and pick the meat from the neck. Chop the boiled egg.
Bring your stock back to a slow boil.
Make a slurry of cornstarch (about 2 tbsp cornstarch and 1/2 c. water -maybe a little more water) - stir it well so it is not lumpy.
While your broth is slowly boiling, drizzle in the cornstarch while you stir. You will see and feel it begin to thicken. If you get it too thick add some plain water or more broth and wisk it. Take it off the heat. The boiling makes the cornstarch thicken. When you get it to the right thickness for your preference add in your giblets and egg.
The giblets should suspend in the gravy. Some will sink but a good thick gravy they will suspend in it.
Serve with dressing.
*giblets = liver, gizzard, heart, neck, fat
** I use the heart for the stock but I don't put it in my gravy. I don't like the texture in my gravy.
Edited to add - if you use the chicken fat for your stock don't chop it for your gravy. Throw it out. Your dog with love it, too.
edited again - If I have them chicken backs cooked with the giblets are good too. The back has some meat and 2 beautiful 'oysters' but the fat gives good flavor.