First, start with a bar of Fels-Naptha. I bought mine at Taylor's Do It Yourself which is a small hometown type of hardware store.
I grated it with my handy grater that used to belong to my grandma.
Then I combined the grated soap with some Borax and Washing Soda. I got the Borax at the grocery store (I've used it for years as a laundry booster). I had to drive to a Kroger to find the Washing Soda. It's not the same as Baking Soda from Arm and Hammer. I found it in the laundry detergent isle.
1 cup grated Fels-Naptha soap
1/2 cup borax
1/2 cup washing soda
Mix together and use 3 Tbl. for a large load of laundry. I made a triple recipe and store it in a plastice container with an old measuring tablespoon in the container.