Can someone help me understand this tutorial?

I try understanding it but as much as i try i just can’t make sense of it, especially the part with th metatables. How do you use them?

Have you taken a look at the metatables API reference? Metatables | Roblox Creator Documentation

Yes I have, it did not help me much, what does it meand by index / indexed? Also are the metamethods the only thing that can be stored in a metatable?

Have you ever seen the error? Thing attempted to Index nil with ":FindFirstChild()" -- Something along these lines. basically __index provides a backup solution in a table when it trys to index nil. Lets say you tried to find a nil value and you set the __index to return false. It will return false.

In addition plenty of tutorials exist on the lovely platform Youtube.

Here is 1 notable tutorial by AlvinBlox. METATABLES - Roblox Scripting Tutorial - YouTube

So __index fires when a nonextisting value is called for in a table? And then you can set it to return a value?

Yes, Heres an example.

local Service = setmetatable({ }, {
  __index = function(table,value)
      return game:GetService(value)



local Vector3 = {}
Vector3.__index = Vector3

function, y, z)
local self = setmetatable({}, Vector3)
self.x = x or 0
self.y = y or 0
self.z = z or 0

return self
so in this case Vector3 is a metatable right?

Yes that is correct, Vector3 is the metatable.