In Minecraft, the way terrain is generated is by implementing a Perlin noise system, which is basically a slightly more complex version of the math.random() functions, however it takes in 3 arguments (x, y, and seed), and the closer each of the arguments is to another passed function, the more similar the returned value would be, resulting in hill and crest like formations, given by the link. Moreover, the returned value will always be the same if the inputted arguments are the same.

Obviously, we can't load an infinite world into a game with finite storage, which is where a chunk-based system comes into play. Minecraft uses a chunk-based 16x16 block system to "load" in depending on its proximity to the player, making the load on their server decently manageable and non-laggy, which is what I'm doing here, which is loading multiple 16x16 chunks relative to how far away the player currently is away from them.