Basically, he tells them to act in a natural way.
He advises her not to go too far with Hamlet.
He tells her not to get too involved with Hamlet or her reputation might suffer if he is unable to marry her. She responds that he shouldn't give hypocritical advice which he himself wouldn't take.
Her father Polonius. Her brother Laertes.
Polonius never gives advice to Hamlet. He interacts with him four times: when he accosts Hamlet in the hall when he is reading (what do you read, my lord? words, words, words), when he comes to tell Hamlet that the players have come (Buz, buz) and during and after the First Player's speech about Hecuba, during the Mousetrap (I did enact Julius Caesar), and to tell Hamlet to see his mother (very like a whale). During these conversations Hamlet constantly has Polonius on his off foot, and Polonius would never have a chance to offer advice. He does, of course offer a lot of advice to his son Laertes, but nobody would confuse Laertes with Hamlet.
Give it to Hamlet so Hamlet will drink it.
Polonius said it to his son Laertes as a piece of advice before he left to Paris
Advice has no singular form; the closest is a 'piece of advice'. Proper usages include: give advice give some advice give a piece of advice
Hamlet tells Ophelia to get to a nunnery. However, "nunnery" not only meant convent but was also slang for whorehouse. It's a matter of interpretation every time he says it which one he means, or whether he might mean both.
The cast of An Obsession with Hamlet - 2009 includes: Leon Ford as Hamlet
The cast of Enter Hamlet - 1965 includes: Maurice Evans as Hamlet
The cast of Hamlet Unbound - 2012 includes: Hugo Santander as Hamlet