To render the fat into tallow, first, put the fat into a big stew pot and add enough water to the pot to just cover the tallow. Add about 1 tbs. of salt for every pound of fat.
You'll notice here that my fat is in very small chunks. The smaller the chunks, the quicker and more efficiently it will render. Ask your butcher (nicely) to run the fat through the grinder if you can, or run it through a food processor. It really makes a big difference! (And don't forget to take them a bar of soap when it's done!)