by 
While OS X may have the reputation of being a solid operating system, it isn’t immune from occasional crashes and app freezes. If you’ve owned a Mac for a long period of time, you’ve most likely come across the spinning beach ball of death a time or two. Here’s how to figure out which app is causing the problem, if you don’t know already, and how to force quit the app:
Click on the icon in the top menu bar and then click on Force Quit… A window will then open with a list of apps. Find the one you want to force close and highlight it. Note that apps that are frozen typically say Not Responding next to them which makes them easy to find in the list. Once you’ve got the app you’d like to end highlighted, click on Force Quit.
That’s all there is to it. The app you selected will shut down completely. You should now be able to re-open it again. If it keeps crashing, try to completely uninstall and reinstall the app as well.
