乐意 means "to be glad/happy to do" — it emphasizes positive, cheerful willingness, unlike 情愿 (would rather, often a difficult choice) or 甘心 (willingness with reluctance or resignation). As an adjective (usually negative 不乐意) it means "unhappy, displeased", differing from 满意 (satisfied with a specific result) and 满足 (content after needs are met).