I'm not overweight, i have strong arm muscles..i don't know what i'm not doing. I can hang, but i can't pullup even an inch, much less all the way. I can do pushups and planks fine, and i do them all the time. I installed a pullup bar in my doorway and discovered i can't do them.
what can i do strengthen more and make this possible?
15 year old girl, by the way.

pull ups require very different muscles, and a great deal of strength when starting from a dead hang. Find a chair or box that you can put your feet at an angle, so that you aren't lifting your entire body weight to begin. Work your way down to a full body lift.

Push-ups are primarily a chest movement, whereas pull-ups require a great deal of back strength.

The best way to get better at pull-ups (or enable yourself to do them) is to keep practicing. Grab the bar and pull yourself as far as you can go. Rest a bit and then go again. That pulling will eventually turn into 1 pull-up. Then 2 pull-ups. And so on and so forth.

Another way to start out is by getting a chair or something to stand on, hold onto the bar with your chin above it and then lift your legs off the chair and try to hold as long as possible. This will help develop the muscles needed to do the actual pull up, by holding the desired position. Once you've mastered being able to hold the pull up position you can work on actually pulling yourself up to that position. If you have someone that can spot you by holding your legs that can help too as you get stronger and more used to it. I was a gymnast and and thats what my coaches did at first to help us learn. Maybe some youtube videos can give suggestions of different exercises to achieve the pull up as well.