Use the above links or scroll down see all to the PC cheats we have available for Minecraft. How to build: make a 3 by 9 minecraft cannon tutorial shape. The open end will be were the TNT goes. Now make an overhang over the unopened end.
But make sure there nothing behind it. Then put water under the overhang. If you did this correctly it shouldn’t go past the 9 block on the open end. After that, put the half slab between the open 9th blocks. Then wire the right side with red stone until there’s one space left. Then wire redstone until 2 spaces are left on the end of the left side. Put 1 more level of blocks in the two empty spaces.