I am a 15 years old medium ly built boy. How can I build my muscles with dumbells fast and what would be the perfect weight for me to lift?

It can't be done "fast".

Woahhh you weigh a lot im so skinny Im a 15 year old boy also and I'm 5'8 and I weigh 110 pounds I cry because of it. But yeah just continuously work out and be consistent with your diet.