To do this, you need to have a blind hem presser foot for your sewing machine.
Step 1: Folding and Pressing Your Hem
Iron it back so the fabric stays how you just folded it.
Fold this under to the desired amount of hem you would like (ours is about 2 inches), so that there is a fold that is created with the fabric right sides together. Iron the fold into place.
Lay it flat again, wrong side up. Take the fold line and line it up so that you only see 1/8 inch of the original hem that you pressed. Press this fold down.
Step 2: Preparing and Using the Sewing Machine
Slide in the fabric wrong side up, and put the foot's plastic straight edge guide right up against the fold. The needle should just barely be piercing the fold of the fabric. Put the needle in the fabric, drop your presser foot, and you can start sewing.
What will happen is the machine will do a little stitching on the part of the fabric you don't see, and then it'll jump over to the right side.
In our example, we used slightly lighter thread so that the stitching is visible to the camera. When you're done, if you use matching thread the hem will be invisible from the right side!