Help a skinny guy out

The good news is that you are still young, so you will continue to grow in size as your body develops. That being said, do you currently do any weight training? Here is a helpful video that describes 5 basic exercises you can do to build muscle, based on compound lifts.
https://youtu.be/HWO2W5c9m7o?si=vzn7Asxzdr8fJ-YC

Jeremy Ethier is a good resource as well for all things fitness. He emphasizes the science behind his methods in his videos.

As far as nutrition, you need to keep eating if you want to get bigger. Find out your TDEE (https://tdeecalculator.net/) which will provide baseline data for you to start from in terms of identifying a target number of calories to consume to gain. Focus on protein primarily, as well as getting enough carbs and healthy fats (avoid the junk food for gaining, as it will only lead to the stuff you don't want. Garbage in, garbage out).

Also, be sure you get enough sleep. That one is really important for gains. You need proper rest for your muscles to recover and grow.

I know that was a rather quick summary of basic tips, but I hope it was helpful in giving some direction. Above all, you will need to stay consistent. That is the only way you can hope to progress and see the results you want. Good luck!