Step 1: Get a Game
Open it with your borwser, i recommend Firefox.
I'll describe howto use firefox, not IE.
Step 2: Open Source of the Game!
then search for the variable which you think is the number/etc you have to enter.
Step 3: Found It
if we look at it, its a number between 0 and 1000, looks familiar... :-P
Step 4: Running Our Little Script
it should tell us the variable's value.
enter the value into the input-box.
if it was the right variable, we should have won.