Using Variables for a Memory Game

Hello all.  So, I've been trying for several days now to create a memory game (similar to the one Bastiaan Timmer made) except with more pairs, 9 pairs in all.  Bastiaan was kind enough to share his source files and I attempted to deconstruct it...but Im just not getting it.

I know I have to use variables and states...and I've managed to create my variable, I know that I have to use a numeric value, and I have gone as far as added the trigger to "Adjust variable by 1 if user clicks on image".

I've looked at all the tutorials on here and I know Im just missing a step...but I just dont know what.

Here is a screencast of what I want to achieve.

I apologize for the rambling  and thanks in advance for your help

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