Shave your soap on the medium-size part of your grater. Place in your storage container. Add 1 cup Borax and 1 cup Washing Soda. You don't have to, but I add about 1/2 cup of regular soda. Stir well with your wooden spoon. Then I seal the container and shake for a few minutes to distribute ingredients evenly. You can make as much as you'd like but be sure and keep within the measurements - i.e. 2 batches - 2 bars soap, 2 cups Borax, 2 cups Washing Soda. Use 1 -2 tablespoons per laundry load, depending on how dirty your clothes are. This is a very low sudsing detergent and is safe for the new front load washing machines. When using Fels-Naptha, it has a clean, citrusy smell. I also add a bit of white vinegar to the rinse cycle, however, you can use your favorite fabric softner. These ingredients used to be difficult to find, but many people are making their own laundry detergent now and they are more readily available. I know one lady who makes it for other people and I now make it for my daughter, too. If you'd like a different aroma, you can add your favorite essential oil while making it.
NOTE: I was told yesterday that if you want your ingredients even finer than the grating, that after you grate it, to put it in the blender for a few pulses. It will disolve either way, it's just personal preference.