Follow this set instructions to create a simple (and working) TNT launcher.
Firstly,make a 7 by 3 area and fill four spaces with TNT (all connecting) and water in the other.
Next,place a button on top of the block next to the water.Then place red stone all along the side until you reach the fourth block of TNT.
Then come out 2 blocks from the last piece of red stone and create a 3 by 3 circle connecting to the block in front of the red stone (this isn't very clear so hopefully you can see what i mean from the photo).
Then place a repeater coming out of the red stone and set it to 4 tics.Place a piece of red stone coming out of that and a repeater to the right of that also set to 4 tics.Then put 3 pieces of red stone around that with a repeater coming out of the red stone set to 4 tics.Then place a block of TNT in front of that (sorry this instruction is also not clear and i don't think anyone could do it without the picture but hopefully the picture guides you correctly).If built correctly you should now have a working TNT launcher (if you hadn't already seen,click the button to activate).Congratulations!