Well on quick chat you are supposed to just type in letters and the letters are in the quick chat box. Well that won't work for me. Could anyone please tell me how to fix this problem.

You have to click on the little speach bubble in order to use quick chat.
I think that's what you're asking.

I know I'm supposed to do that but then something will pop up and I can't say anything I want to. I have to say things that are programed in it.

You can't quick chat a sentence you come up with your self you have to use what's in there.
If you press enter while in the quick chat menu a search menu come up and if you enter a word here it will give you all the sentences with that word in it.
Another thing to note if you are selling or buying something and are using the quick chat option to sell or buy the item,
you can hit F11 to repeat your last quickchat sentence, thus saving you the trouble of having to click on it everytime you want to say something.
Of course the repeat option isn't limited to only buying and selling but that's what it is used for the most.

hopefully that helps.

My friend does not have to look through the sentences. He just types in a sentence and then it happens.

What world do you play on?
If i'm hearing correctly, you might be on a quick chat world- you can only use preset sentences on those worlds.