TENS units are simple and safe to operate. The doctor will provide the correct settings and show you how to use it, and then you can take it home and use it yourself as needed.
TENS units use at least two electrodes to pass current through the body. The electrodes are typically adhesive pads that will stick to your skin. The electrical current will pass from one electrode to the other, so the positioning of the electrodes enables you to control where the electricity goes.
The process is safe and painless because the electrical current used is such a low voltage.