ok so first make a n like thing 1 block tall 3 blocks long and 5 blocks going foward then put water in it and at the end put a half slab put a lever in the block separating the sides next put redstone to the block before thehalf slab put lever on the side of the half slab put the tnt on the half slab and the 2 blocks before it pull the lever you placed first then 2

thanks for you time this was for people that don't know how to