screen shot file you newb.. my screen shots automatically go to my desktop because I use the shift alt f3 thingy
I suggest downloading either LightShot or Gyazo, I recommend Gyazo as it has a history setting of all the screenshots you take, gives you links to them that you can go to, save/copy the image, etc.
Press finder then press go at the top left hand corner then option on your keyboard go into library the Application support Minecraft then Screen shots.
Well what I do is when i take the screenshot i press the link that shows.. I use Gyazo take the pic of the rule breaking then post it on here
I find it by going into my recourse pack folder, then in the top left corner it says .minecraft, click that and it will take you to your minecraft section, then click screenshots.
Click finder then up at the left corner at file edit view then click go while your in go press option on your keyboard then it should show library then application support minecraft screenshots.
well I'm more of windows guy, but I'm gonna have to get used to using a mac when I'm at my dads house. but thanks