So, you want to create a custom menu for SpaceEngine.

We can start by looking at the default menu scenario file, which is in data > scripts > Scripts.pak archive.
Open the .pak file with your preferred zip manager, go to the menu folder, and extract the scene1.se file. That's the script file for the default menu scene.

You can save it into an addons subfolder, for example, by placing it into an addons > MyMenu > scripts > menu folder.

When you open it with a text editor, you may notice the relevant part of the menu:


Now we need to find a location for our custom menu. Go to the desired place with your camera, then save the location with the Locations menu (F6), by clicking Add > This location, just as we learned from the Tutorial (You did the tutorial, right?).



Let's get the script for this location by using Share > Copy script code to clipboard, then paste the content into the text editor.
This will be the result:

You can see that the code for the menu scene is basically identical. To use this location on the menu scene you only have to copy:

and substitute this:

Then save the modified scene1.se file.
If you have placed the file where suggested above, next time you run SpaceEngine your location saved in addons will be the scene used by the program.

You can play with the other variables available in the scene1.se file, for example to change the speed of time (TimeScale command[spaceengine.org]), field of view (FOV command[spaceengine.org]), and others.