Pec Workout

I can barely even ride up the smallest hill. My arms are easily building muscle doing various things but my legs are just soft. I’m a 15 year old male.

I’m a college student studying to become a law enforcement officer. I not much into going to the gym cause I don’t have much time because of all the studying . I’ve really thought about taking up cycling to help build muscle and strength. Does anyone have any tips on how to get started?