You can start with this, learning about procedural noise algorithms such as Fractal Noise (basically compounding perlin noise): https://devforum.roblox.com/t/creating-procedural-mountains-a-fractal-noise-tutorial/1494362
^ math.noise uses perlin noise btw
If you want to create a random-number-generator with a local seed and be able to support large numbers & decimals, use Random.new()
Developer Forum | Roblox
Creating Procedural Mountains This tutorial will cover generating procedural terrain using various types of noise as heightmaps. We will blend noise together to create convincing "Minecraft" style terrain. I will give you code snippets, diagrams and explanations so that hopefully you can recreate this yourself, and explore other types of terrain...