All you need is an 8 oz bar of soap, glycerin, and water. Well also a really BIG pot, something to mix it with, a grater and some containers to store it in.
The only trouble I had was finding the glycerin... I went to my local grocery story,... they had glycerin suppositories (NOT what you want), and apparently my local Walgreens stopped carrying it. I ended up borrowing some from my mother-in-law... but next time I will try Michaels or Joann's. Maybe I'll have better luck there.
It turned out pretty well, though it does have a slightly weird consistency... kind all stays together, which helps when you're trying to pour it into containers with small openings. I would maybe recommend a funnel. The other thing I noticed is that the water sinks to the bottom when you store it but just shake it up before you refill your pump containers and you should be good. It makes a LOT of soap, so pick a scent you like and have fun!