Do //pos1 to set the origin where you're standing. It'll be the bottom left corner of the map region, which will be pasted towards positive coordinates (+X/+Y/+Z).
Do //load tutorial_map to paste the map
Create an arena (e.g. /arenas create block_league tutorial)
Enter the arena editor
Go to Players and disable teams
Set min and max players to 1
Go to Spawners and set the spawn point standing on the node indicated in the picture. If you set the spawner incorrectly, the tutorial won't work!
Go to Settings -> Arena properties and set arena_mode to 0
Optionally go to Customise -> Background music and put a track. Suggested track: Non-Euclidean Geometry by Punch Deck (CC BY 4.0)
Enable and leave the editor (remember to set the entrance)

Updating the map

Server admins

Just in case the map needs an update (e.g. found some holes, improved some areas), this is the position you should stand to load the schematic again: https://i.imgur.com/meEZn6a.mp4

Builders

Select as pos1 the node that server admins use and as pos2 something around 40-50 nodes above that, on the opposite corner of the map
Run //save tutorial_map; confirm with //y
Move the file created with the same name in <worldfolder>/schems into <modfolder>/bl_tutorial/schems