How do you close a program in Andriod.  For example, Google Play.  The only way I see to close it is to hit the Backspace button.  So if I've been browsing Google Play, that could be 5, 10, 20 clicks to get back to the original screen.  I've noticed the same with virtually every other application too.  I just don't see any option to "Close" or "Exit" most of the programs on my smartphone.  
On a PC, all apps have a way to close them.  On the smartphone running Android I don't see a way.  I'm admittedly ignorant at this point, but willing to learn.

Google Android is build on making use of 100% of RAM, so they don't believe you need to 'close' or exit an app, as you might want to go back into that same app at any future moment. But the OS will free up that memory if a newer app requires it.

Of course this causes issues if the app you left is still working in the background even though you don't really need or want it to.

 

On older versions of the android OS some users ran Task Killers. 

On newer versions of android you can simply open the "Recent Application Menu" on most devices by tapping the ' □ ' (open square) on the menu bar and then sliding the recent app you want removed from memory "off the screen" to close it.  

 

Note, some manufacturers change the menu key assignment for Recent Applications so check your manual.

If you need to "FORCE Close" an app or reset it, then you do that through SETTINGS / APPS.