Mel,
I had the TENS treatments before, for a fractured finger
(that never healed right & is still 'bent').
You use the lowest settings for pulse and intensity, then gradually increase them until you feel a 'tingle' & is not uncomfortable.
Stay at those settings - or back off 1 setting.
You may want to play around at the pulse rate, but never more than is comfortable. Keep it going for anywhere from 5-10 mins to 1 hour and see if you get relief.
The pads have 'sticky-backs' gel is not necessary.
Hairy areas should be shaved for best stick/contact.