In what way is one allowed to open tin cans on Shabbat and Yom Tov?
If he empties out the can immediately and throws it away, and he doesn't mean to continue using the can, it is permitted since it's a one-time use. But if he leaves the food in the can, it is forbidden to open it unless he ruins the can beforehand, e.g. making a hole on the bottom. Rabbi Dov Lior