Pretty well. My mom and I used to make it when I was a kid. Most recent was about 15 years ago when I made my own solo. I used 100% pig fat from pork and bacon drippins, and plain old lye. I can't find the recipe but it was pretty simple.
Basically you render the fat and clean it out by boiling it with water and letting it settle out a few times to get rid of salts and crud. You mix up the right amount of lye with the right amount of water for the amount of fat you have, get them to the right temperature, and stir them for a while until the saponification is well under way. I used a hand mixer to keep it stirred up. You pour it into a mold, which can be a glass baking dish or whatever, let it set for a while, and cut into bars.
It has to cure for a few weeks before it's ready to use. Mine has an excess of lye, so it's too harsh for bathing but really good at cleaning tough grease. It smells good too.