"you will fly when you click a fly button and you control it by where you look"

-- LocalScript inside a ScreenGui with a TextButton named "FlyButton" 
local flyButton = script.Parent.FlyButton
local player = game:GetService("Players").LocalPlayer
local character
local flying = false

local function toggleFly()
    if character then
        flying = not flying
        local humanoid = character:FindFirstChild("Humanoid")
        if flying then
            flyButton.Text = "Stop Flying"
            humanoid.PlatformStand = true
        else
            flyButton.Text = "Start Flying"
            humanoid.PlatformStand = false
        end
    end
end

local function fly()
    if character and flying then
        local humanoidRootPart = character:FindFirstChild("HumanoidRootPart")
        local camera = workspace.CurrentCamera
        local direction = camera.CFrame.LookVector
        humanoidRootPart.Velocity = direction * 50
    end
end

flyButton.MouseButton1Click:Connect(toggleFly)
game:GetService("RunService").Heartbeat:Connect(fly)

player.CharacterAdded:Connect(function(newCharacter)
    character = newCharacter
end)

character = player.Character or player.CharacterAdded:Wait()