How would you do "Minecraft" like terrain generation?

I want to make terrain generation like in minecraft with places where there is flat surface and places where there are mountains. However while i was using perlin noise and looked at all roblox terrain generation examples i noticed that you can only make it either have tons of mountains or just a flat surface. I looked up on google and it said that i need to use multiple octaves but i dont know how to do that in roblox. Anyone knows how to do it?

This is a very complex system. To perform this, you would have to have algorythms that change the frequency of the generation system. Here's an example from the wiki:

local seed = math.random()
local width = 200
local length = 200
local amplitude = 20
local frequency = 25
 
for x = -width/2,width/2 do
	for z = -length/2,length/2 do
		local y = (math.noise(seed,x/frequency,z/frequency) * (amplitude/2)) + (amplitude/2)
		workspace.Terrain:FillBlock(CFrame.new(x*4,y*2,z*4),Vector3.new(4,y*4,4),Enum.Material.Grass)
	end
end
 

Now, to make the different frequencies, we can do this:

amplitude = amplitude + math.random(-1.0,1.0)
frequency = frequency + math.random(-1.0,1.0)

And that makes:

local seed = math.random()
local width = 200
local length = 200
local amplitude = 20
local frequency = 25
 
for x = -width/2,width/2 do
	for z = -length/2,length/2 do
		local y = (math.noise(seed,x/frequency,z/frequency) * (amplitude/2)) + (amplitude/2)
		amplitude = amplitude + math.random(-1.0,1.0)
		frequency = frequency + math.random(-1.0,1.0)
		workspace.Terrain:FillBlock(CFrame.new(x*4,y*2,z*4),Vector3.new(4,y*4,4),Enum.Material.Grass)
	end
end

Hope this helps!