The right half of the brain controls the left side of the body, and the left side of the brain controls the right side of the body.
In most people, the left side of the brain is better developed, so the right hand is stronger and more controllable than the left hand. But sometimes, the right side of the brain is more developed; then the person is left-handed.
Less than one person in six is left-handed. No one is sure why so many more people are right-handed. It’s possible that the reasons go back to the days of the caveman.
A person who was born right-handed would fight with a weapon in his right hand and use his left hand to shield himself; a left-handed person would fight with his left hand and shield himself with his right hand.
A person who uses his left hand to shield himself protects his heart, which is on the left side of the body. So, many right-handed persons who were wounded would survive, while left-handed persons would suffer wounds around their heart and die.
Over the course of evolution, this higher survival rate among right-handed persons could have led to more persons being born right-handed.