At the respawn of your game, put signs down that resemble these so the player knows to only go here if they have died already.
Wherever you want a checkpoint, put an iron door down, a lever, and a sign next to it instructing the player what to do. Then dig straight up from that spot and put water at the bottom.
Make a tunnel to the checkpoint hole, or to the door if the checkpoint is above ground. Place a sign telling the player which checkpoint it is.
Tell the player what to do if they came down to try to get ahead. You can make a ladder back to the top but I was a bit harsher.
The creator of this guide has not included tools