The same way as other painters: by brushing oil paint onto a surface, which in his case was a wood panel.
Leonardo da Vinci studied the human body
he studied at home
he studyed it in France he was hily skilled at the age of 15 and then moved on
At the age of 15 Leonardo had already mastered skills in the fine arts and the young man was sent to Florence to work as an apprentice in the renowned workshop of Andrea del Verrocchio I got this...