I grew up as a boy doing soldering kits in the 80s. I wanted to do the same for my daughter so bought a soldering iron online.
It came with a box of orange resin with Chinese writing on it. I'd never seen something like this to do with soldering. Running it through Google translate comes with something like 'solder additive'.
When I google search online for 'solder additive' I get vague descriptions of better joints, or coping better with dusty joints. I don't understand how that would be solved by resin.
My question is: What does solder additive do?
EDIT: Thanks for all those that contributed to this question and the EE SE community. I asked my Dad what we had done for resin when I was growing up. He responded, "We used resin-core solder, that's why you never saw the resin."