The minecraft INVedit hack is the easiest to use out of any inv editor minecraft has. The download link is below and the video explains how to use it step by step. It works for both singleplayer and multiplayer (if you have the perms). Some of the minecraft cheats help you find things faster and get to them quicker than others, this one just sticks it straight into your inventory, easy huh?
You can download INVedit here