to have a deep and thorough understanding of something; to be highly proficient or expert in a subject

to be proficient in; to be familiar with

to know something thoroughly or be well-versed in a specific subject or skill

to not know how to swim; to not be a strong swimmer

to have an understanding of how the world works or to be experienced in the ways of the world

thoroughly conversant, skilled, or well-versed in a specific task or field

lacking experience in the ways of the world or social conventions; naive and unsophisticated