Although he had not yet decided to become an artist, Monet was making extra money at age 15 drawings caricatures which he signed O. Monet. He sold these at a local store for 10-20 francs a piece. They were often depictions of his teachers and his fellow students would purchase them. Part of this may have been his dislike of school. Instead of paying attention he would doodle in the margins of his books. That is how he developed his proficiency. Perhaps it was even rebellion against his family. His father most certainly disapproved of the act and young Oscar Claude Monet never quite got along with his father. His talent was evident in these caricatures and a professional artist, Eugene Boudin, took notice.
Because the caricatures showed talent, Boudin did not want him to continue in that vein. Boudin insisted that the unwilling Monet should learn the art of landscape painting en plein air with him. Eventually that is exactly what Monet did and it set him in the path of becoming the Impressionist painter that history now remembers.
Caricatures may also have influenced him in his future style. Caricatures pick a few elements and focus on them disproportionately. Perhaps this would apply later to his paintings as he would observe elements and then focus on them, painting something realistic yet surreal.
Sketch of Woman and Umbrella
Waterlilies at Giverny