A "Workbench" is a block only available in Alpha mode. It is used to craft items such as blocks, tools and other resources.
To obtain a Workbench, use your inventory crafting grid (2x2) and place 4 wood blocks inside (one in each slot). Right clicking on a Workbench will open a 3x3 crafting grid where you can create new recipes. A Workbench is essential in order to advance far in the game. It is even necessary for the mining of ores, as picks can only be crafted with a Workbench.
When a workbench is mined, even without a tool, it can be picked up, to be moved or stored.