Can I trade in my car while still making payments on it?

Yes you can

Thanks guys cause I'm trying to do my car

Yes. Positive equity on your current car works like additional down payment. Negative equity is added to the amount financed on the new one.

Yes. (I did). You'll have to make up any difference on what they'll buy it for and what is still owed on the note. Hopefully you'll be above water!