I'm teleported into the ground and I don't understand the meaning. Is there a law or order to set up teleports correctly?

You need to go on either side of the door and set teleport point using the /setteleportpoint command, I assume what is happening to you is, you have not set the teleport points causing you to be teleported to 0, 0, 0

After experimenting with different settings, the door teleported to the underground world was completed.

I'll give it a little try more, thank you.