Your xye game folder has a sub-folder called levels, you can place the level file in this folder. Then restart Xye and you will find the new level in the list
The usual installation creates a (hidden) folder called .xye in your user home folder. Get a file browser and go to /home/yourusername/.xye/ find the levels subfolder and copy the new level folder to that location.
The new subfolder in which levels are placed is $XDG_USER_DATA_HOME/xye/levels . Normally it is ~/.local/share/xye/levels
If you have any level that you made in the editor and would like to share, feel free to email it to vexorian@gmail.com and it might be featured in the blog.