I bought one of those tortilla keepers not too long ago, but threw away the packaging (pic included so you'll know what I'm talking about). So I have no idea how to use it, since this will be my first time.

Do you microwave the tortillas first and then put them in the keeper? Or do you microwave the keeper with the tortillas inside?

You use this just to keep the tortillas warm. So, after the microwave. By the way tortillas are so much better when they are warmed on a griddle!!

Yep, I do mine on the griddle sometimes too