If you played, you noticed that the world generation is a set of consistent (10-20) steps. First formed biomes, then they cut out the cave, then filled with water, and then planted grass, etc. Every stage is a separate complicated algorithm. And in fact, this know-how of the game, which is its cost. If these algorithms were simple and known, then we would have a bunch of clones Terrarium.
But in General there is nothing complicated. You just need to sit down and think how you specifically for your particular game, given the gameplay and other things, it will be easier to implement it. And this job is somewhere at the intersection of main programmer and designer.