Boys smell when they go through puberty because increased hormones cause you to sweat a lot more. This can make your body pretty stinky, especially under the arms or between your legs.
Body odor starts early in puberty. Using an antiperspirant/deodorant can help control sweat and stinky odors.
Try using an antibacterial soap when you take a bath or shower. This can get rid of some of the bacteria that can lead to body odor.