Step 3: Find soap, insert into bag
This one is pretty self explanatory, but... here goes.
By now you should have a mesh bag, open on one end and sealed on the other, and a bar of your favorite soap.
Open the unsealed end of your mesh bag, and then insert the soap lengthwise. Why lengthwise? Personal preference. I also think that it helps water run off the bar easier, resulting in faster drying times, and you don't want the mesh to be stretched too tightly against the surface of the soap, otherwise it will cut into it.
For best results the mesh should be able to sit loosely across the surface of the soap where it can shave off bits of dry soap, producing a thicker lather.