How can I make a Block that generates items in there storage?

Im pretty new. So I wanted to make an ore generator. I want that it generates items after a certain amount of time,  but I cant find out, how I can generate items exactly in the block that I want. I only find procedure templates like put items in current open GUI, but I don’t want to keep the GUI open. It‘s like after 30sek you can get copper out of one slot, after 1min coal out of another slot and so on. But how can I choose the GUI where the items generate, without being in it?