ok but what counts? i use it to explain the thing the teacher explained badly, and then i do the homework myself. is that cheating? because if it is then so is youtube

That's not cheating, that's a tutor. The line most schools have landed on is: using it to understand is fine, using it to produce is not. The problem is the line's invisible on the page. A paragraph you understood and a paragraph you pasted look the same, which is why Ms. Harmon can't tell, which is why she's asking.