A person who is right-handed is more dextrous with their right hand than with their left hand: they will write with their right hand, and probably also use this hand for tasks such as personal care, cooking, and so on. Approximately 90% of the population is right-handed, while most of the remaining are left-handed. A very small percentage of the population can use both hands equally well; a person with this ability is deemed to be ambidextrous.
Throughout history being right-handed was considered normal (the Latin word dexter meant "right" and is associated with skill). Hence the many prejudicial connotations became associated with right handedness: skilful, diligent, dextrous, deft. The associated left brain hemisphere that is said to be more active in right-handed people, has been found to be correlated with linguistic and logical skill.
In German schools decades ago and in some American schools, left handed children were forced to write right-handed.