Growing potatos in potato bag

This is my first one, and Ive kinda got the gist of how it should work, but I have some questions. When first planting do I fully cover the spouts or leave them poking up a bit? After that, at what point do I add more dirt, and how much dirt? For example do I wait until it is good and leafy, and then cover the green completely? Cover the green partially leaving some leaves poking out? That kinda thing. Thanks for the pointers :)