In this scene from Hamlet, young Laertes has just received permission from King Claudius to return to school in France (in scene 2). Here his father, Polonius, gives him some fatherly (and quite famous) advice on how he should behave when he is away from home.
Polonius tells his son that his character is very important, and the he should make sure his actions and words mimic a strong character. He reminds him that it is good and important to have friends, but make sure that these are good friends. When you meet a new friend, beware that it may end in a fight ("Of each new-hatch'd, unfledged comrade. Beware of entrance to a quarrel"). However, he warns, if you get in a fight, make sure you're the man people fear to fight. He tells Laertes, "Give every man thy ear, but few thy voice" which reminds him that it is more important to listen to what people have to say, and take in their opinions, than to be the one talking. It is important that he dresses well, so he should spend as much money on his clothes as he car- provided that the clothes are not tacky- because people will judge the value of a man based on what he is wearing. Do not borrow or lend money because it will ruin friendships and make you week.
Polonius concludes with the most famous line of his speech by telling his son above all the rules he has outlined, it is important that Laertes be true to himself.
This above all: to thine own self be true