I learned how to make lye by accident - I put too much potash on my potato plants and it killed them so I dug up what potatoes I could and my arms turned bright red and burned. I put vinegar on them to neutralize the alkaline.
As far as how to find that info - just Bing it - step by step - homemade lye, rendering fat, soap making. A lot of info that is most helpful is from Mother Earth News - :) - those hippies in the 1970’s that went back to earth have perfected some great ideas.
It is all fun - my neighbors however, think I am a bit strange.....
Yes, Mother Earth had good stuff but as liberals will, they ate themselves up and if you want skills and info go to Backwoods Home Magazine (make sure it has home in it.) then get the "whole shebang" all past issues in books year by year and a subscription.
THE biggest plus is they are right leaning/liberatarian instead of leftists like Mother Earth. I'm reading year 5 now, that is during the Clinton years and the editors point of view is heart warming.
So invest your money with the right leaning mag Backwoods Home Magazine. They also have gun experts (gasp) who write columns. Learn from those who have DONE it, not just read about it.
Another resource is the Foxfire books. You can buy them thru BWH or see if your library has any.
Tho in bad times you will want copies in your library.