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You're looking at some suet right there. Because it's a fat, it's useful in just about any situation where you need fat. Because it's from a cow, though, it's going to have a pretty strong flavor, though kidney fat is typically more mild than fat from other parts of an animal. If it were from a pig, you'd be looking at leaf lard, but from a cow it is suet.
Most people, if they know about suet, know one or two things. First, it's used to lure birds to a bird feeder in a particularly effective if messy-on-a-hot-day way. Some suet mixed with seeds makes a treat that many birds adore. So you could make bird food out of it, but that would be a waste.
Another bit of suet lore is from a poem by Lewis Carroll, Father William:
"You are old," said the youth, "and your jaws are too weak
For anything tougher than suet;
Yet you finished the goose, with the bones and the beak
Pray, how did you manage to do it?"
(The secret was a career in law earlier in life, if you're curious.)
Personally, I wouldn't eat pure suet, but apparently old people had few choices in 19th century England. Fortunately there are more uses than just for the birds and the elderly.
Beef suet is great for adding fat to otherwise lean beef dishes. If you are making hamburgers, sausage, or some manner of beef stew, and you used a lean cut of beef, then you could fortify the dish by adding the suet. Hamburgers and sausage really need a goodly amount of fat in them to work at all, so the beef kidney fat is a really good addition there. A hearty stew, like a chili, would probably work well with the extra fat, because you want to convey all of the flavors from the spices well, which requires fat in many cases.
Of course, you could just use a fattier form of beef rather than the suet, but you have a couple of reasons not to do that. First, the kidney fat is milder in flavor than other portions of the fat, so you can control the flavor of the final dish a bit better.
Second, you can more easily control the amount of fat, as 80% lean chuck doesn't necessarily mean you're getting 20% of fat by weight. It just means you're not getting any more than 20% of the fat.
Third, you may have access to meat from an animal that doesn't have much fat, such as venison. I have my own personal vendetta against deer that I won't go into here, but I highly recommend people start eating more venison. The suet will give you more options of what you could do with that meat.
Aside from fortifying lean meats, you have a few other options as well. If you need to make a roux for thickening a beef stew, you could use the suet instead of butter or another fat. People tend to think of roux as a butter/flour combination, but it works with any kind of fat.
If you wanted to be a bit more creative, you could make a pastry dough with the suet. I do not recommend this for any kind of a sweet pie. Seriously. But there are a range of savory pies that would go marvelously with a more savory crust, especially if they have a meat filling.
Those are some basic ideas to get you going on using your kidney fat. Once you've tasted it once or twice, you'll get a better feel for its flavor profile, so you'll be ready to know the limits on where it will and won't be good. Have fun, and enjoy!