The Pinwheel means your Mac is thinking. If you have small RAM on your computer, you might see this more often. If your Mac doesn’t respond its never a good idea to manually power off but in some cases its necessary. In most cases Force Quitting the Application seems to do the trick. Just hold the Command + Option + Escape key (esc) then click the app you would like to quit then click “Force Quit” This is similar to Ctrl, Alt, Delete Task Manager on a windows computer.