"create a level system with xp and data store and that can change players health and weapon damage"

-- main script in ServerScriptService 
local DataStoreService = game:GetService("DataStoreService")
local levelStore = DataStoreService:GetDataStore("PlayerLevels")

game.Players.PlayerAdded:Connect(function(player)
    local folder = Instance.new("Folder")
    folder.Name = "leaderstats"
    folder.Parent = player

local xp = Instance.new("IntValue")
    xp.Name = "XP"
    xp.Value = 0
    xp.Parent = folder

local level = Instance.new("IntValue")
    level.Name = "Level"
    level.Value = 1
    level.Parent = folder

local success, errorMessage = pcall(function()
        local data = levelStore:GetAsync(player.UserId)
        if data then
            level.Value = data.level
            xp.Value = data.xp
        end
    end)

if not success then
        print("Error loading data: " .. errorMessage)
    end
end)

game.Players.PlayerRemoving:Connect(function(player)
    local success, errorMessage = pcall(function()
        levelStore:SetAsync(player.UserId, {
            level = player.leaderstats.Level.Value,
            xp = player.leaderstats.XP.Value
        })
    end)

if not success then
        print("Error saving data: " .. errorMessage)
    end
end)

-- script for adding XP and leveling up 
local function addXP(player, amount)
    local stats = player.leaderstats
    stats.XP.Value = stats.XP.Value + amount

local currentLevel = stats.Level.Value
    local requiredXP = currentLevel * 100

if stats.XP.Value >= requiredXP then
        stats.Level.Value = stats.Level.Value + 1
        stats.XP.Value = stats.XP.Value - requiredXP

player.Character.Humanoid.MaxHealth = 100 + (10 * stats.Level.Value)
        player.Character.Humanoid.Health = player.Character.Humanoid.MaxHealth

local weaponDamage = player.Backpack:FindFirstChild("Weapon")
        if weaponDamage then
            weaponDamage.Damage.Value = 10 + (2 * stats.Level.Value)
        end
    end
end

-- example of usage 
game.ReplicatedStorage.AddXP.OnServerEvent:Connect(addXP)