Open the Crafting Table
Place 1 Iron Ingot in the top-middle slot
Place 1 Stick in the middle-left slot
Place 1 Stick in the center slot
Place 1 Stick in the middle-right slot
Place 2 Strings in the top-left and top-right slots
Place 1 Tripwire Hook in the bottom-middle slot
Take the Crossbow from the result slot