How do i save my leaderstats?

You need to use the DataStore Service

Here is the script.

local players = game:GetService("Players")
local datastore = game:GetService("DataStoreService")
local ds1 = datastore:GetDataStore("PowerValueSaver") --Runs power server
local ds2 = datastore:GetDataStore("MoneyValueSaver") --Runs money server

players.PlayerAdded:connect(function(plr)
    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "leaderstats"
    leaderstats.Parent = plr

    local Power = Instance.new("IntValue")
    Power.Name = "Power"
    Power.Parent = plr.leaderstats
    Power.Value = ds1:GetAsync(plr.UserId) or 0 --Checks if power is saved or sets to 0
    ds1:SetAsync(plr.UserId, Power.Value) --Saves power

    local Money = Instance.new("IntValue")
    Money.Name = "Energy"
    Money.Parent = plr.leaderstats
    Money.Value = ds2:GetAsync(plr.UserId) or 0 --Checks if Money is saved or sets to 0
    ds2:SetAsync(plr.UserId, Money.Value) -- Saves Money

    Power.Changed:connect(function()
        ds1:SetAsync(plr.UserId, Power.Value) --Saves when Power is changed
    end)
    Money.Changed:connect(function()
        ds2:SetAsync(plr.UserId, Money.Value) --Saves when Money is changed
    end)

end)