Instructions
Right-click the crafting table inside your open. This causes a pop-up to appear, displaying a 3-by-3 grid beside a large square.
Place a piece of cobblestone in all but the bottom two squares of the center column. Mine regular stone with any kind of pickaxe to get more cobblestone.
Place a bow in the center square of the center column. Place three pieces of string and three wooden sticks on another crafting grid to craft a bow.
Place redstone dust in the last remaining square. Mine redstone ore, located near the very bottom of the map, using an iron pickaxe or better to obtain redstone dust. When you place all of the cobblestone, the bow and the redstone in the grid, a picture of a dispenser block appears in the large square.
Click the dispenser square and drag it to your inventory to complete the crafting.