Ever wonder how much processing power or memory certain apps are taking up in your Mac? Or maybe you want to know how much data an app is using just like you can on your phone. There is a useful utility in Mac OS X called Activity Monitor that will show you all of that.
All you need to do is click the magnifying glass in the top right corner of your screen to do a Spotlight search. Top in “Activity Monitor” and open it. You can then click on the options at the top of the Activity Monitor window (CPU, Memory, etc.) to see what impact each application on your Mac is having on each of these components. 
