Why does my DataStore save everything as 1? [NOT ANSWERED!]

If you want to save multiple values to the same datastore, you will need to wrap them in a table. I have modified your code to show how this could be done:

--//variables
local DataStoreService = game:GetService("DataStoreService")
local LevelStore = DataStoreService:GetDataStore("Levelllssss")


--//player added
game.Players.PlayerAdded:Connect(function(player)
    -- Get the levelstore data into a variable (levelInfo)
    local success, levelInfo = pcall(function()
        return LevelStore:GetAsync(player.UserId)
    end)
    if success then
        -- If there was no data, then setup levelInfo with default values
        if not levelInfo then
            levelInfo = { Level = 1, NeededXP = 1000, XPP = 0 }
        end
    else
        -- Error retrieving data from datastore
        player:Kick("Data Error | Please rejoin!")
    end

    --//creating level folder
    -- Avoid using the parent option of Instance.new, as it can cause lag. Prefer to setup your object and then parent it manually
    local LevelFolder = Instance.new("Folder")
    LevelFolder.Name = "LevelStore"
    LevelFolder.Parent = player

    --//Creating level
    local Level = Instance.new("IntValue", LevelFolder)
    Level.Name = "Level"
    Level.Value = levelInfo.Level

    --//creating needed xp
    local NeededXP = Instance.new("IntValue", LevelFolder)
    NeededXP.Name = "NeededXP"
    NeededXP.Value = levelInfo.NeededXP

    --//creating current xp
    local XPP = Instance.new("IntValue", LevelFolder)
    XPP.Name = "XP"
    XPP.Value = levelInfo.XPP

    -- No need to save data here. If the data was nil then you're just saving default values, which is not needed,
    -- and if it wasn't nil, you're just saving the same info the datastore already contained back into it
end)


--//Save when player leaves
game.Players.PlayerRemoving:Connect(function(player)
    local levelInfo = { Level = player.LevelStore.Level.Value, NeededXP = player.LevelStore.NeededXP.Value, XPP = player.LevelStore.XP.Value }
    local success = pcall(function()
        LevelStore:SetAsync(player.UserId, levelInfo)
    end)
    -- Need to deal with data failing to save
end)

Note that if you are testing this in play solo in studio, the game will exit before anything gets saved. If you create a local server in studio or try it in a published game then everything will work correctly. Also, I recommend following the tutorial on this page for your data saving code. This will give you much more robust error handling.