The two lines on your CBFM test sticks are for LH and Oestrogen. As your Oestrogen rises, funnily enough the corresponding line gets fainter.
A rise in Oestrogen will signal that ovulation will follow at sime point in the next few days, but not necessaily immediately. The monitor will now watch out for your LH surge, at which point the LH line does get darker..
Incidentally, if Oestrogen rises quickly, you can jump straight from low to peak....its all part of the learning curve for the monitor.
www.peeonastick.com gives you some great reads about it and some sample oics of sticks for you to compare.
Good luck....I love my CBFM and it certainly helped get me pg last time!