Use the synaptic packet manager in order to install yacc / lex. If you are feeling more comfortable doing this on the console just do:
sudo apt-get install bison flex
There are some very nice articles on the net on how to get started with those tools. I found the article from CodeProject to be quite good and helpful (see here). But you should just try and search for "introduction to lex", there are plenty of good articles showing up.
Source: Stackoverflow.com