To see how tin keeps a steel can from rusting, get an empty can. A can from canned green beans or canned peaches or something like that would be good. Wash the can and use a can-opener to take off the sharp top so you don’t cut yourself, and recycle the top.
Check that this is really a tin and steel can, and not an aluminum can – use a magnet, like a fridge magnet. If the magnet sticks to the can, then it’s got steel in it. If it doesn’t stick, that’s an aluminum can. Go get a steel can.
Now use sandpaper to rub the shiny surface off the outside of one part of your can. Try to scrape off the tin and leave just the steel underneath. Get the can wet, and then leave it in the air to dry. Or just leave the can out in the rain for a week or two. When you come back, which parts are rusty?