simple question

Hi everyone

I'm trying to make a parser (not a compiler) for a language, and I´m
learning to use flex and bison.... but in this moment I just don´t
know what to do:

I know that I can define the token "Keyword" , but .......is it
useful? I mean, when I make the rules in Bison I need to know which
keyword is it, and it'll be all the time....(is not the same IF than
RETURN or END). I's supposed that flex is the one who compares the
words,,,,,,

the other option I though was defining each keyword in the flex file
but that is a lot of work to do and a lot of tokens to recognize.....
I've read many manuals but I really don't know what to do...

I hope my question is well-explained and thanks for your help

: )