Build 3 stones like this
Put an upsidedown stair
Set 2 stones like this
And a block on the other side
Set a redstone on the stone block and a redstone torch
Shift click on redstone torch to place a iron trapdoor there
Put water on the trapdoor and tripwire hooks
Connect the tripwire hooks with string
Stand like this under the water and hold right click!
Now its done! i hope you enjoyed the gude!
The creator of this guide has not included tools