Recently, news broke out that modders can now create custom maps and play with them on Dark Souls. That's an exciting piece of news, but gamers should be forewarned not to get too excited.
Proof of Concept
The custom map was created by modder Horkrux. The map used is the Crossfire map from the game Half-Life. The team behind the mod uploaded the map as a proof of concept—merely showing that importing custom maps into the game is possible.
However, 'possible' doesn't mean practical. The mod was made possible in a very roundabout way, and it will take a long time before every guy could introduce their own maps on their own copies of Dark Souls.
User u/Katalash explained the mod's limitations concisely on a reddit thread. The main roadblock, according to Katalash, is the development tools FromSoftware use for their games. "Souls games use Havok for physics and collision detection," says Katalash, "and [FromSoftware] added their own customizations on top of the format."
FromSoftware also used a different version of the engine between games. Even the engine for Dark Souls and its Remastered version are different.
The custom map was made through years of the team effort, with modders Meowmaritus and Horkrux on the front lines. In layman's terms, Meowmaritus created tools that allowed custom models to be imported into the game, while Horkrux made the physics of those models to work.
Modding is a collaborative hobby, and communities develop around games with specific goals and visions. In Dark Souls' eight years of existence, various mods have been developed for different purposes like graphics correction, HUD UI improvements, texture patches, among others.
Dark Souls' modding community is currently focused on making the custom map work. Prior to this proof of concept, modders were able to import Demon Souls maps to Dark Souls. This is the first time a map from a completely foreign environment was put into the game.
However, the proof of concept showed the current limitations of what modding could do. There is a visible lack of enemies on the map. Although adding models on the map would be an easy task for them to do, those enemy models would stand around and do nothing.
For enemy models to become interactive, modders will first have to give them what is called navmeshes. NPCs use navmeshes to understand how to navigate the environment they're in. Modders currently haven't developed this to populate their maps with enemies.
While the rest of the gaming community celebrates this achievement and give words of encouragement to the modders, you could help contribute to the cause by learning how to mod yourself. On the PC, you could start with this tutorial on Steam.
When you already know the basics of modding, join the Discord group of the Dark Souls modding community to learn from the experts. From here, you could give input and produce your own mods that will help the community improve the current mods we have so far.