How do you EXIT full screen mode in Yosemite?

Click the minimize/maximize button a second time or press Control-Command-F simultaneously. The button can be green or grey depending on how you have configured the appearance under the General pane of System Preferences.

To resize window, simply double-click window bar.

The best way to do this that I have found is to put the cursor in the upper left hand corner and wait a second. The green button reappears (you also get the top bar back in case you want to do other things than change the view.) and you can click on it to get back to normal view.

Push the mouse cursor up to the top of the screen and the 'traffic light' buttons will reappear and allow you to leave full screen. I know, completely intuitive.... Escape key also works for me.

Also note, that if you hold down the "option" key when you hit the green "full screen" button, it will "maximize" instead.

Now if there were only a way to reverse that. I almost never want to go "full screen"