I am going hunting with a buddy on his property and he told me that he didn’t know if I needed a license or not. I was wandering if I need to purchase one for this outing?

I have been shooting and hunting for over 15 years and am very well versed on firearms safety and operation. I would like to offer lessons to new shooters in the area, but don’t know if a license is required to do so.
It would not be for anything official. Just a service to teach proper handgun safety, how to shoot, etc… Then let them shoot a variety of different handguns.

Say I wanted to buy a used one from a friend, would he be legally obliged to check for a license? What if he doesn’t? Does he get in trouble, or me, or both?
Please, only UK answers. I know America/other countries have different laws, that does not help me.

I just bought a handgun and was wondering how much cost to the to check background and to give me the license? I guess all of that was include on the price because I didn’t get charge for anything else. I live in Florida.