If you don't want to use any third party software give yourself ingame a structure block. With help of them you can select an area of max 48x48x48 that you may export to a .nbt file. This is saved in the world folder under generated. This works very good if you want to export none large struktures. You can do it the same way to reimport this .nbt file on the same or other worlds - that works even better than with WorldEdit or McEdit.



For larger objects (for example islands, cities, full world...) you could zip your world save and upload that. As Planet Minecraft has got a maximum data file size you may need to upload a large world to a cloud and make a reference on Planet Minecraft to this.

For Linux: To publish a map exit the world(DO NOT FORGET TO FINISH IT OR AT LEAST DO 5%) and then make backup, then open backups folder and copy the archive of the backup(this can be done on windows too) and then click the Minecraft page of this site.
From there you should go to maps, click Post Map and then do whatever you want(insert the zip as downloadable file or insert it in a alternate download).
BY THE WAY DO NOT FORGET TO PUT INVENTORY AND GAMEMODE WHICH WILL PLAYERS HAVE BEFORE LEAVING

Leave the world where you want the player to start and put yourself in the correct gamemode. Other solution is to edit the level.dat file and remove the player compound. You can achieve this using nbtexplorer or texelelf's nbtedit filter for MCEdit https://vshare.onl/

Click the content button with the green arrow above your name, then click "create new," then select map and add images, the map, description, name, and exctra.

you made me curious about it too, so i did a quick google and found this.

hope it helps in some way :)

https://www.youtube.com/watch?v=tJOMDMRt0Xs