The holes. I found these videos helpful enough to bookmark when I was learning:

https://www.youtube.com/watch?v=8jRmQvw0i1Y

https://www.youtube.com/watch?v=jGquWRxB57o

https://www.youtube.com/watch?v=_s4xYxU_BfI

I think people do it differently, and there are different patterns, so you can go either way as long as you do it consistently. On the corners, I put the hook into the chains of the previous row.

I'm an experienced knitter and can do the basic crochet stitches (SC, DC,TC, etc.) But I cannot seem to get the hang of a granny square. I can't seem to see the places the hook needs to go and the patterns are hard to read.

Does the hook actually go into stitches or the "holes" in the square, for one?

Any tips? I've watched several videos.