"create a level system with xp with data store and that changes players health and the damage of the players weapon"

-- main script (ServerScriptService) 
local DataStoreService = game:GetService("DataStoreService")
local levelDataStore = DataStoreService:GetDataStore("LevelData")

local function onPlayerAdded(player)
    local success, errorMessage = pcall(function()
        local levelData = levelDataStore:GetAsync(player.UserId)
        if levelData then
            player.leaderstats.Level.Value = levelData.Level
            player.leaderstats.XP.Value = levelData.XP
        else
            player.leaderstats.Level.Value = 1
            player.leaderstats.XP.Value = 0
        end
    end)

if not success then
        warn("Error loading data for "..player.Name..": "..errorMessage)
    end
end

local function onPlayerRemoving(player)
    local success, errorMessage = pcall(function()
        local levelData = {
            Level = player.leaderstats.Level.Value,
            XP = player.leaderstats.XP.Value
        }
        levelDataStore:SetAsync(player.UserId, levelData)
    end)

if not success then
        warn("Error saving data for "..player.Name..": "..errorMessage)
    end
end

game.Players.PlayerAdded:Connect(onPlayerAdded)
game.Players.PlayerRemoving:Connect(onPlayerRemoving)

-- local script (ServerScriptService) 
local function onXPChanged(player)
    local xp = player.leaderstats.XP.Value
    local level = player.leaderstats.Level.Value
    local nextLevelXP = level * 100

if xp >= nextLevelXP then
        player.leaderstats.Level.Value = level + 1
        player.leaderstats.XP.Value = xp - nextLevelXP
        player.Character.Humanoid.MaxHealth = 100 + (10 * level)
        player.Character.Humanoid.Health = player.Character.Humanoid.MaxHealth
    end
end

game.Players.PlayerAdded:Connect(function(player)
    player.leaderstats.XP.Changed:Connect(function()
        onXPChanged(player)
    end)
end)

-- weapon script (inside weapon model) 
local weaponDamage = 10

local function onActivated(player)
    local level = player.leaderstats.Level.Value
    local target = -- get the target humanoid
    if target then
        target.Health = target.Health - (weaponDamage + (level * 2))
    end
end

script.Parent.Activated:Connect(onActivated)