To take a screenshots in Skyrim, there are two ways:
To take a screenshot, all you need to do is press the printscreen button (PrtScr). When you take the screenshot, you'll notice a short, one second pause in the game.
This will save your screenshot in your game directory. It should be located in: [ Steam\steamapps\common\skyrim\ folder ], which should be in C:\Program Files\ or C:\Program Files (x86)\ unless you have installed Steam to a different directory.
If it doesn't work, try checking Users/(username)/My Documents/My Games/Skyrim [ skyrim.ini ] file and make sure, bAllowscreenshot function is set to 1 instead of 0.
-----------------
Also you an take screenshots and save them to your Steam screenshot manager by pressing the F12 button.
This only works if you have the Steam community overlay enabled. !!!
When you take the picture, Steam will inform you with a small pop-up and sound.
------------------
As for the FPS counter, you can try this: http://www.nexusmods.com/skyrim/mods/24239/?(the simplest counter you can get. lol)