Do in tutorial mode
Go forward until you reach Dolphin lake, there is a platform in the center with stairs leading to it. There is a chest here with a bunch of items in a square and two Axes. Grab everything then use the crafting table here. Goto the mechanisms tab, and press down on the beacon icon to select sea conduit. Make this then go forward into the water, place this ON TOP of the wooden block. Now use the axe to cut the block down.