Ask for beef tallow at my supermarket, and they give you beef fat to render down. Put the fat into a slow cooker and let it slowly melt out. At some point, you can strain out the connective tissue and pour the fat into a container. As it cools it turns opaque white. Use it to cook with, just as you use butter and bacon grease. Lamb tallow is also nice.
The same thing applies to pork fat, but it’s harder to come by, because there’s a market for it in the form of lard. The most prized pork fat is the leaf lard from around the kidneys, but in my view, any pork fat is great.
Unlike bacon grease and butter, lard and tallow don’t have a very strong flavour. Instead, they enhance the flavour of the foods cooked in them. McDonald’s fries were tastiest, apparently, back in the days when they fried them in tallow, and the fries have never been the same since they were forced to stop using tallow. Cooks I know greatly prefer the flavour of pie crust made with lard, instead of Crisco.
But of course lard and tallow will kill us just from being in the same room . . .