From Latin placēre 'to be agreeable' and ultimately PIE *pleh₂k- 'to be flat', the word captures the ancient metaphor that what is smooth and unobstructed is pleasing — a root shared with 'placid', 'placate', and 'plaza'.
As a verb: to give pleasure or satisfaction to. As a polite adverb: used in requests to add courtesy, short for 'if you please' or 'it pleases you'.
From Middle English 'plesen,' from Old French 'plaisir' (to please, to be agreeable), from Latin 'placēre' (to be pleasing, to satisfy), from PIE *plāk- (to be flat, smooth, calm — hence pleasing, without disturbance). The root *plāk- also generated Latin 'plācidus' (calm, gentle), source of 'placid,' and 'plānus' (flat, smooth), source of 'plain' and 'plane.' The pragmatic use of 'please' as a polite imperative softener — 'please sit down' — developed in Early