The down one works by the water at the bottom stopping your fall. You just need to dig a hole all the way down, place a sign and a bucket of water above the sign. The sign stops the water running out and the water breaks your fall.
The up elevator takes a bit more work, dig a seperate hole all the way down again. Place signs on the wall to stop the water running out. If you don’t have blocks around you can use fence gates too. Then place a bucket of water at the top block of the hole so it runs all the way down. You’ll then need to grab some kelp from the kelp farm, place it at the bottom of the solid water column and place kelp every block up the water column. This will turn the running water in to water source blocks. Then go back to the bottom and destroy the bottom of the kelp and it will break the column of kelp. Finally, mine the block at the floor level of the solid water colum and replace it with soul sand. This will create a bubble column which shoots you up quickly.