What I have done was to download the single player map and the minecraft server from Mojang.
Install the server then and copy the map to the world folder.
Launch the server and let it get compiled, then stop it.
Finally, you will need to archive the folder into a .tar.gz format, 7zs should do the trick.
Transfer the file into the archive directory of your sever.
In had to upload it to my /home folder then cp to /var/games/minecraft/archives.
The UI can import from there.