i need help with a health system ?

something like this?

player.Stats.Level.Changed:Connect(function(player)
    player.Character.Humanoid.MaxHealth = player.Character.Humanoid.MaxHealth + 50
end)

this is my stats code

local DataStore = game:GetService("DataStoreService")

local Data_Key = 0

local Level_Data = DataStore:GetDataStore("Level"..Data_Key)
local Exp_Data = DataStore:GetDataStore("Exp"..Data_Key)
local Strength_Data = DataStore:GetDataStore("Strength"..Data_Key)
local Defense_Data = DataStore:GetDataStore("Defense"..Data_Key)
local Stamina_Data = DataStore:GetDataStore("Stamina"..Data_Key)
local DevilFruit_Data = DataStore:GetDataStore("DevilFruit"..Data_Key)
local DevilFruit_Owned_Data = DataStore:GetDataStore("Owned_DevilFruit"..Data_Key)
local SkillPoint_Data = DataStore:GetDataStore("SkillPoint"..Data_Key)

local Start_Level = 1

game.Players.PlayerAdded:Connect(function(Player)
    local UserId = Player.UserId

    local Stats_Folder = Instance.new("Folder",Player)
    Stats_Folder.Name = "Stats"

    local Level = Instance.new("IntValue",Stats_Folder)
    Level.Name = "Level"
    Level.Value = Level_Data:GetAsync(UserId) or Start_Level

    local Exp = Instance.new("IntValue",Stats_Folder)
    Exp.Name = "Exp"
    Exp.Value = Exp_Data:GetAsync(UserId) or 0

    Exp.Changed:Connect(function()
        if Exp.Value >= 500*Level.Value then
            Exp.Value = 0
            Level.Value = Level.Value+1
        end
    end)

    local Str_Stats = Instance.new("IntValue",Stats_Folder)
    Str_Stats.Name = "Strength"
    Str_Stats.Value = Strength_Data:GetAsync(UserId) or 0
    local Def_Stats = Instance.new("IntValue",Stats_Folder)
    Def_Stats.Name = "Defense"
    Def_Stats.Value = Defense_Data:GetAsync(UserId) or 0
    local Stamina_Stats = Instance.new("IntValue",Stats_Folder)
    Stamina_Stats.Name = "Stamina"
    Stamina_Stats.Value = Stamina_Data:GetAsync(UserId) or 0
    local DF_Stats = Instance.new("IntValue",Stats_Folder)
    DF_Stats.Name = "DF"
    DF_Stats.Value = DevilFruit_Data:GetAsync(UserId) or 0

    local Skill_Point_Stats = Instance.new("IntValue",Stats_Folder)
    Skill_Point_Stats.Name = "SkillPoint"
    Skill_Point_Stats.Value = SkillPoint_Data:GetAsync(UserId) or 0

    local DF_Owned = Instance.new("StringValue",Stats_Folder)
    DF_Owned.Name = "DF_Owned"
    DF_Owned.Value = DevilFruit_Owned_Data:GetAsync(UserId) or "None"
end)

game.Players.PlayerRemoving:Connect(function(Player)
    local UserId = Player.UserId

    local Stats_Folder = Player:WaitForChild("Stats")
    local Level = Stats_Folder:WaitForChild("Level")
    local Exp = Stats_Folder:WaitForChild("Exp")
    local Strength = Stats_Folder:WaitForChild("Strength")
    local Defense = Stats_Folder:WaitForChild("Defense")
    local Stamina = Stats_Folder:WaitForChild("Stamina")
    local DF_Stats = Stats_Folder:WaitForChild("DF")
    local DF_Owned = Stats_Folder:WaitForChild("DF_Owned")
    local Skill_Point = Stats_Folder:WaitForChild("SkillPoint")

    Level_Data:SetAsync(UserId,Level.Value)
    Exp_Data:SetAsync(UserId,Exp.Value)
    Strength_Data:SetAsync(UserId,Strength.Value)
    Defense_Data:SetAsync(UserId,Defense.Value)
    Stamina_Data:SetAsync(UserId,Stamina.Value)
    DevilFruit_Data:SetAsync(UserId,DF_Stats.Value)
    DevilFruit_Owned_Data:SetAsync(UserId,DF_Owned.Value)
    SkillPoint_Data:SetAsync(UserId,Skill_Point.Value)
end)

So you have a few issues. A big one being you're not using datastores, if you don't know what those are, they're what saves your player data so when they leave and rejoin, all of their money/health/level doesn't get set to 0. Heres a useful video to learn about datastores: youtube.com/watch?v=DkYupSBUpes

I'm not going to teach you about datastores, but I will tell you how to make the players health increment.

Another small thing is that you're not using variables, which bugs me a little bit.

1. Add a RemoteEvent in ReplicatedStorage

2. Add the script into ServerScriptService

3. Add the local script into StarterPlayer>StarterPlayerScripts

Script in ServerScriptService

-- Gets the remoteEvent.
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local remoteEvent = ReplicatedStorage:WaitForChild("remoteEvent")

-- Sets the data.
game.Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:Connect(function(character)
        remoteEvent.OnServerEvent:Connect(function(player, level)
            local humanoid = character:WaitForChild("Humanoid")
            local moneyPerLevel = 50 -- Variable incase you want the players health to go up by more than 50.

            local function update() -- Made a function in case if you want other things to happen when they level up.
                humanoid.MaxHealth = moneyPerLevel * level
            end

            update()
            print("Players MaxHealth: "..humanoid.MaxHealth) -- Debugging...
        end)
    end)
end)

Above, is the setter. Like its name, it will set the data. Meaning, it changes the health to what it is supposed to be at.

Local Script in StarterPlayer>StarterPlayerScripts

local player = game.Players.LocalPlayer

-- Gets the remoteEvent.
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local remoteEvent = ReplicatedStorage:WaitForChild("remoteEvent")

-- Gets the level.
local statsFolder = player:WaitForChild("Stats", 100)

local level = statsFolder:WaitForChild("Level")

-- Fires it so the data doesn't equal 0.
remoteEvent:FireServer(level.Value)

-- Checks if the value changed, if so, fire the remoteEvent.
level.Changed:Connect(function()
    remoteEvent:FireServer(level.Value)
end)

Above is the getter. I don't think I need to explain how this works, it's just the opposite of the Script...

I hope this helped you, if it did, please mark this as the accepted answer to help other people. If you have any questions then comment!

ALSO: I recommended renaming your stats folder from Stats, to leaderstats. So you can use the built-in Roblox leaderboard...