He warns her not to trust Hamlet's declarations of love.
He warns her to watch out for Hamlet, because his protestations of love may be merely designed to seduce her.
Laertes, in a parallel revenge, seeks revenge against Hamlet for killing his father, Polonius, and the early death of his sister Ophelia. Hamlet does die, but not before Laertes, so Laertes never does get his revenge against Hamlet
It shows most dramatically in Scene 16, (Act 4 scene 5,) when Laertes leads a mob to storm the castle.
It illustrates Laertes close relationship to Ophelia.
Laertes accuses Claudius of killing his father Polonius in Act IV, Scene V.
Laertes.
To France, so he can spy on Laertes.
I can't give you a response unless I know what he is supposed to be responding to. "Thanks Rosencrantz and gentle Guildenstern" is a response to what those two guys tell him at the beginning of Act III Scene I for example..
Hamlet to Laertes, who's choking him in his sister's freshly dug grave: "I prithee take they fingers from my throat." Hamlet naturally picked the least appropriate time possible to be polite.
In the last scene of the play, before Hamlet and Laertes are to have their swordfighting match, Hamlet makes a prepared speech of apology beginning with the words "Give me your pardon, sir. I've done you wrond, but pardon it as you are a gentleman." He goes on to say that if he ever did anything to offend Laertes, it was something he did when he was crazy. It's a convenient excuse which nobody buys.
setting
Setting