Minecraft wiki entry for Beginner%27s_guide, associated text: The right button is more complex: This is the "Use" command, with effects that depend not only on what you're pointing at, but on what you're holding. There are special blocks (such as the "crafting table" discussed below) which open a GUI when used, but if you are not pointing at one of these, you just use whatever you currently hold. There are various tools that are used for their respective purposes, but at first you're probably holding a block of wood or dirt, and the "use" of a block is to place it down into the world. Simple blocks like these can be placed on any surface of a block that's already in the world, but more complicated blocks such as flowers can be put only in particular places (e.g. the top of a grass or dirt block). If you are pointing at a block that does have its own use, but you want to place a block on it (instead of, say, opening the GUI for a crafting table), you can "sneak" while placing the block.