Im scronny and i want to be fit * partly built* how should i work out?

i have 1 weight t its a 10 pounder.im a 15 year old male. im scronny and i know its going to take a while but want to biuld musccle do push ups work? stand ups? sit ups? so would i get bigger if i just did all of those with out the weight? or do i NEED the weight? how should i start? i feel un healthy and want to be able to defend my self if i get in a fight in the future