'Versed' means knowing a lot about something, and knowing it well enough to use it, not just having heard of it. It almost never stands alone. It travels with 'in' and, nearly always, with 'well': 'well versed in tax law', 'well versed in the rules of the game'. You can also hear 'poorly versed' or 'not well versed', which is a polite way of admitting you do not really know a subject. This is a formal, slightly bookish word. You would meet it in a job advertisement, a report, or a newspaper, and not usually in a chat with friends — a friend would say 'she really knows her stuff'. Because it sounds respectful, people often use it to praise someone's knowledge without sounding like they are testing them. One small oddity: although it looks like the past tense of a verb, there is no ordinary verb 'to verse' behind it in this meaning. It comes from an old Latin idea of turning something over — the way you turn a subject over and over until you know it. (Young people do say 'let's verse each other' for playing against someone, but that grew out of 'versus' and has nothing to do with this word.)