Dumb questions

Hi, I dont travel much but am planning on taking a trip on September and I have some stupid (probably common sense) questions!

1) does a backpack count as a carry on? Whats the difference between a personal and a carry on?

2)can I put a duffle bag inside a suitcase and bring that as a carry on? (Cause im planning on buying a lot so wanna bring the extra suitcase without having to pay for it to get there yn?)

3) how much time before my flight do I need to be to the airport?

4) I tend to carry some of my prescription medication in a little capsul in my pocket so i dont gotta carry a whole bottle. Can I take that through tsa or do I suck it up and bring the whole pill bottle?

Thank you in advance! Sorry if these are hella stupid lol.