Gather 1 dispenser, 1 button or lever, 1 water bucket, 1 flint and steel, 1 block of your choice, 1 redstone dust, 1 redstone torch, and TNT
Place a solid block as the base
Place a dispenser facing forward on top of or into the base
Place water in front of the dispenser where the TNT will launch from
Place TNT inside the dispenser
Place a block behind or beside the dispenser
Place redstone dust connecting the dispenser to the power source
Place a redstone torch or use a button/lever to power the dispenser
Activate the redstone to fire the TNT
Repeat and adjust the layout for stronger or longer-range shots