Your desktop is a ƒolder on your startup disk (or boot drive); that is to say the hard drive or partition that you are running the Operating System from whenever you boot your Mac.
Re: Using key commands to take pictures -- each operating system uses a different naming scheme, e.g picture1, picture2, OR screenshot1, screenshot2, etc.
Go to Finder Preferences (under "Finder" on top left of screen adjacent to the Apple) and select the 3rd tab. check DESKTOP.
Now via the Finder sidebar you can click to access your desktop screenshots if you do not see them on your Finder desktop.
I suspect that your desktop is highly cluttered.
Here is some unsolicited but invaluable advice:
The desktop is a ƒolder within your Users ƒolder.
BUT, it has one special characteristic that no other ƒolder has.
OS X allocates RAM to every file, folder, icon, etc. that exists there.
To free up RAM and to speed up boot time (disabling extraneous fonts helps a lot too) and to speed up Finder operations in general, create a ƒolder at Root Level on the boot volume of your Mac's Hard Drive. Name it "Desktop Detritis" or whatever you wish. Move everything from your desktop there, and move applications to the Applications ƒolder. Then drag that folder to the right side of your Dock. Voila.
There is a very good book called "Degunking Tiger" that describes this and many many more tips like it.
Also I suggest using xSlimmer to regain a ton of space on your hard drive. Also I use (either) "Omni Disc Sweeper" 1.5.2 or "WhatSize" 10.3.92 to show me the HUGE invisible files that are clogging my Macs, e.g. huge Swap Files. If you use Adobe applications or do heavy duty work in Desktop Publishing, Photographic work, Graphic Images, MIDI, etc. you may have invisible Scratch Disks of a Gigabyte or two in size. I also use FileBuddy9 or TidyUp! to search out duplicate files and delete them.