Handedness, the ability to use a hand (left or right) more efficiently is linked to orientation in the brain. The brain is made up of two hemispheres (sides), the left and the right. People tend to have one hemisphere specialisation. The specialised hemisphere is dedicated to speech and language, among other functions. People with right brain specialisation tend to be left-handed and people with left hemisphere specialisation right-handed.
There is no clear explanation for why some people are left or right-handed. There is a small genetic link; if both parents are left handed there is a slight chance of having left handed children.
people have suggested that left-handed persons are more intelligent. I don’t know if that is true, but there are some famous intelligent left-handed people like Albert Einstein, Leonardo Da Vinci, Marie Curie and Barrack Obama.