From Quake Wiki
The worldspawn entity is a special entity that defines all the static geometry in a Quake level, along with various settings of the level, such as its title, the music played and other things. The worldspawn is always the first entity defined in a .map file, and in game, always the first entity loaded.
Note that the first table lists only the keys supported by the original engine and compile tools. Modern compile tools and engines very frequently use keys stored in the worldspawn entity to do things the original tools and engines did not allow. Since the supported keys differ between different tools and engines, some of the most common keys are listed in a separate table below. Non-standard keys are usually prefixed with an underscore, which causes engines that do not support them to ignore them.
|message||This is the text that will be printed to the console when the level loads. It is used for the level name, though some level designers also include their name. As an example, E1M1, the first real level of episode 1, has the text "The Slipgate Complex" as the value for this key.|
|worldtype|| This sets the ambience of the level. Depending on this value, some entities will play different sound effects, and the key items will display differently.
|sounds|| The number of the cd track to play. If using the original Quake music, valid tracks are 2 to 11.
Many modern engines support external music files. Usually a file named with the same number as the specified CD track will be loaded, if it exists. For example QuakeSpasm will try to load the file music/track02.ogg if sounds:2 is specified. The exact location of the file lookup as well as the audio formats supported depend on the engine. Most commonly supported is Ogg Vorbis.
|light||The ambient light level. The light tool uses the value of this key to determine the minimum value of light in the level.|
|wad||A string that tells QBSP where to look for wad files so that it can include the textures in the .bsp file it outputs|
|_sunlight||Brightness of the light coming from any sky brushes in the level.|
|_sun_mangle||Sets the angle of the sun using pitch, yaw and roll.|
The worldspawn entity has no spawnflags.