"create a running script that allows player to jog by double tapping W and sprint faster by hold shift while jogging"

-- local script 
local UserInputService = game:GetService("UserInputService")
local player = game.Players.LocalPlayer
local character = player.Character
local humanoid = character:WaitForChild("Humanoid")
local shiftHeld = false
local wCount = 0
local canRun = true

local function inputBegan(input)
    if input.KeyCode == Enum.KeyCode.W then
        wCount = wCount + 1
        if wCount == 2 and canRun then
            canRun = false
            humanoid.WalkSpeed = 20
            wait(0.3)
            canRun = true
        end
    elseif input.KeyCode == Enum.KeyCode.LeftShift then
        shiftHeld = true
    end
end

local function inputEnded(input)
    if input.KeyCode == Enum.KeyCode.W then
        wCount = 0
        humanoid.WalkSpeed = 16
    elseif input.KeyCode == Enum.KeyCode.LeftShift then
        shiftHeld = false
    end
end

UserInputService.InputBegan:Connect(inputBegan)
UserInputService.InputEnded:Connect(inputEnded)

while wait() do
    if shiftHeld and humanoid.WalkSpeed == 20 then
        humanoid.WalkSpeed = 30
    elseif not shiftHeld and humanoid.WalkSpeed == 30 then
        humanoid.WalkSpeed = 20
    end
end