For everyone who says they can't make a gravy- if it is because you have no patience to stand there and stir, stir, stir to make sure it all gets incorporated and not burn (yep, that's my problem, same reason I can't make pudding on the stove top- I always try to rush it) the microwave is your new best friend.
Here is the basic white sauce (medium) I got from a cookbook long ago and how I change it up depending on what I am making.
In an 8 cup Pyrex glass measuring cup for each cup gravy melt 1 Tbsp butter (you can use pan drippings or oil or whatever- and you can use less than called for). You can use fat-free stock or bullion to make it fat free. Add 1 Tbsp flour and whisk the daylights out of it.
Microwave on high for exactly 45 seconds, no more, no less. This is whether you are making 1 cup of gravy or 6. (6 is the most you can make in the 8 cup Pyrex.)
Whisk the crap out of it again and add any seasonings you might like and then add 1 cup liquid- milk, stock, 1 cup water one bullion cube, whatever you like and microwave 2 minutes. Whisk again. Keep nuking and whisking 2 minutes at a time til it is boiling and at your desired consistency.
You cannot mess this up, it is perfect every time. You can make a basic gravy with butter and stock or milk for cream gravy then add pan drippings at the end if you desire.
This is way better than any you can buy in a can, mix or jar, and you know exactly what is going into it.