anondog how does giffgaff know I've introduced that person?
The member must activate the sim you've given them, which bears an activation code. Provided you obtained that sim properly from your Spread giffgaff allocation, giffgaff will know that sim came from you. However, don't give out sims that came from a shop, or in the box with a phone. Those are not part of your Spread giffgaff allocation and will not earn any payback.
anondog what is the reward structure
You'll find the details if you expand the Cash in your Pocket section of https://giffgaff.com/super-recruiter