"Acting on something" meaning ?

Normally you'd try to not think about porn and not to get aroused to avoid PMO. Which is a good idea, however it may not be possible at all times. Instead of fearing those thoughts/feelings and running away from them, you can also accept them. Because the thoughts are not the problem, the actions you usually take because of them are. So you just take away the final link from thought to action, instead of trying to control everything. That takes less willpower.
So you feel the urges but yet do not take action because of them. That is "not acting on your urges".

Obviously you shouldn't be sitting alone in front of your screen for hours taunting your urges, although it is empowering. Use it among other techniques and use your willpower not only to not masturbate but also to DO go out for a jog or something.

 

You are acting because of urges, but not on the urges, which would be doing what they are urging you to do.
At least that is what is meant.

Great idea to do that by the way.