You don't necessarily need to use them. "Hear, hear!" is the correct phrase. It is an enthusiastic expression of agreement. It means "Listen to what that person just said." Similar expressions are "Indeed!" and "Well said!" and "You can say that again!" and "She hit the nail on the head!" All of them are a little old-fashioned. "There, there" is used in comforting someone who is upset or hurt. It is a kind of nurturing phrase used by a mother to a child. "There, there, don't worry, that's just a scratch, we'll put a band-aid on it and it will heal soon." "Here you go!" and "There you go!" are a cheerful acknowledgment that you've just given someone what they asked for.

That's all very well.....however, the phrase "I hear what you say" means anything but what you might think it should mean, coming from a UK native speaker. Please refer: (http://www.independent.co.uk/voices/i-hear-what-youre-saying-but-ill-ignore-it-1357551.html)