Simply hover over or click one of the item icons and it will display a description on the left side of the screen! If you see an item or gun in-game but don't know what it does, hover over it and discover what it does.
The cheat sheet currently has all guns and items from the game.
At the top right corner you'll see a seach box which you can type keywords into and it will filter down the entire list of items to only show relevant ones based on what you typed. Try typing anything you want in there, not every key word currently works but I'll continue to add keywords as I'm adding more pages!
Information and stats about each gun/item is taken from a combination of my own personal experience with the game, watching people play and from the Official Wiki. There's a chance you may find incorrect information as a result of patches changing the game or my own incompetence, but I would like to keep it as accurate as humanly possible, so would greatly appreciate any corrections or extra information you may have. You can contact me via twitter @eluc_ or shoot an email to firstname.lastname@example.org.