"That's what this is. A whole world created to raise her son and protect him until somebody came to rescue him."
Su'Kal's world was a holographic program created by Doctor Issa for her son Su'Kal in the mid-3060s while they were stranded on Theta Zeta. The mother intended this world to be a place where her son was raised and protected until rescue came.
Set within a holodeck in the crashed KSF Khi'eth, the "planet" had two moons. By 3189, the planet had an overcast sky with thunderstorms.
The two moons were likely meant to mimic those of Kaminar.
It was inhabited by holographic programs who were there to teach Su'Kal on many subjects, so he could be prepared for the day when he went outside, and gormaganders. Over the decades, as radiation ravaged the systems of the starship, programs began malfunctioning and, in some cases, stopped running.
The program would disguise any other individuals who entered it as part of the program and as different species, causing Michael Burnham to appear as a Trill, Hugh Culber to appear as a Bajoran, Saru to appear as a Human, and Adira Tal to appear as a Xahean. This had the unfortunate side-effect of disguising personal effects, including anti-radiation medication; when Adira snuck off the USS Discovery and onto the Khi'eth to bring extra medication to the away team, they were forced to carry the medication in their mouth. Though Gray Tal only existed as a consciousness within the Tal symbiont, since he was appearing to Adira when they boarded the Khi'eth, the program detected him and gave him a visible appearance as a Vulcan.
When Su'Kal became frightened, he would hide in an island fortress from the other programs. Saru eventually convinced Su'Kal to shut the program down. (DIS: "Su'Kal", "That Hope Is You, Part 2")