How to make sure an app IS closed on a Mac
I've been working with Macs since 2006, and one of the things that took me a while to realize is when I exit an app on Mac (coming from being a Windows user since Windows 3.1) is when I would click on the red button (upper-left corner of the screen), that I assumed that the app was exited.
What I didn't realize is, that even though an app disappears from the screen, it is not closed and out of memory. This mistake can eat up available memory and make a Mac slow down.
When exiting a Mac app, always use the ⌘Q key combination. This insures that the app is closed and not using any available RAM.
* BONUS TIP:
Here's another tip. Along with the above, you can also use the ⌘W and the ⌘Q key combinations to make sure an app is closed and out of memory (handy, when using QuickTime and don't want a previous video to play if someone else opens the app later).