Whats a module script, whats different from normal scripts?

Module scripts are mainly used to store functions that are used in multiple scripts in games. Unlike regular scripts, module scripts only return one value that's returned when you require the modulescript.

One example: people use module scripts to store their datastore functions so they can use them in multiple scripts without having to rewrite the function in each script. Example:

local DataStore = {}

local PlrData = {
    level = 1, 
    xp = 0
}

function DataStore:AddPlayer(Plr)
    local MyData = Data:GetAsync(Plr.UserId) or {}
    MyData.Ah = MyData.Ah or "Yes"

    PlrData[Plr.UserId] = MyData
end

function DataStore:RemovePlayer(Plr)
    if PlrData[Plr.UserId] then
        Data:SetAsync(Plr.UserId, PlrData[Plr.UserId])
        PlrData[Plr.UserId] = nil
    end
end

return DataStore

So then, you can require the module script from another script and use the functions as normal:

local DataStore = require(modulescript) -- require the module script 

for I, V in next, Players:GetPlayers() do
   DataStore:AddPlayer(V)
end

Players.PlayerAdded:Connect(DataStore:AddPlayer)

if not game:GetService("RunService"):IsStudio() then
    Players.PlayerRemoving:Connect(DataStore:RemovePlayer)
end

Hope this helped. If you have any questions comment below :)