The traffic lights explained

What do the ‘traffic light’ buttons at the top-left of every window actually do? If I hit it minimises the window, and the yellow button seems to do the same. But hitting is not the same as clicking the red button. The latter sometimes closes the app and sometimes just shuts the window. And as for the green button, it seems to randomly change the shape and size of the window and there isn’t any keyboard shortcut that I know of. Alan Gilpin The red button isn’t the same as

it’s the same as which is ‘close window’. In apps that only ever have one window (such as Notes), and do the same thing, but in apps that allow for multiple windows, repeatedly hitting will leave you with no windows, but the app itself will still be running, as shown by the Dock icon and the menu bar. The green button is called Zoom and it toggles the window size between the minimum size it needs to be to display the current contents properly, and the last size you set it to. There’s no shortcut for it by default, but apps that support it have a menu item on the Window menu to activate it. Apps that can’t be zoomed show the green button greyed out. If you really want a keyboard shortcut for this you can create one in Keyboard Preferences. In Yosemite, the green button has been changed to trigger the full screen mode in apps that have one.