I never used the so-called sock stop or latex before so here are the istructions on how to use sock stop or latex:
1. Cut out the areas you want to paint with latex from cardboard. This is simple when you made the slippers for yourself: You just draw the shape of your feet on the cardboard (doesn't have too precise) and cut it out.
2. If you like you can draw the pattern you want on the slippers on the cardboard to try it out. Otherwise just draw it from your mind. (Some nice patterns are e. g. hearts, clouds, paws or just dots).
3. Put the cut-outs into the slippers, turn them around and paint the pattern on the back.
Be sure to use a paper or something similar to protect the surface you're working on from the latex.
4. Leave it to dry for about 24 hours so you can be entirely sure it's dry. VoilĂ !
P. S. If you want the latex thicker you can also add another layer after about 12 hours of drying