A can is a cylindrical shaped container. Tin is a natural resource metal. Some cans used to be made from tin, so you may hear the phrase "tin can" or tin for short.

Technically the are the same. However we usually refer 'can' as a can drink/food in liquid form e.g. a can of coke, a can of vegetables soup whereas 'tin' refer to solid food such as a tin of sardine, a tin of pineapple chunk and a tin of Danish cookies.

Mojave, I don't understand your grandma's saying..

Now if she said it while dancing the Can-Can it would be much funnier.

There's a funny saying my Grandmother used to say: Can what you can and what you can't can, put in little round tins.