In this comic play, the title character, Charles Marlow, is conflicted about his role as a gentleman, with its constant pressure to perform and meet rigid standards of both manners and masculinity. As a result of feeling uncomfortable, and especially feeling under pressure to act the role of the courtly lover and find a wife, Marlow becomes timid, tongue-tied, and self-conscious when he is around upper-class women.
However, the timidity disappears around lower-class women. Not feeling under pressure to meet a standard, he can be himself with the servant class. Kate Hardcastle, herself of the upper classes, realizes this when Charles is misled to mistake her home for an inn, her father for an innkeeper, and herself for a barmaid. She then pretends to be a barmaid, because this way, she can get to know the real Marlow and he can get to know her under relaxed circumstances.
The phrase "she stoops to conquer" contains a witty oxymoron or seeming contradiction. Conquering someone implies overpowering them or standing bigger and taller, not stooping. Stooping implies servility. Yet in this case, the so-called servant becomes the master or mistress of the day by using her wits to woo and win the man she wants to marry. The title suggests that sometimes, people need to bend or strategize to get what they want.