Custom Character Controller - Adding Foward and Backwards?

I have been working on a custom character controller script, and I wanted to use W and S to go foward and backwards. I have been following the wiki but I am kinda lost on this part.

local player = game.Players.LocalPlayer
local RunService = game:GetService('RunService')
local ContextActionService = game:GetService('ContextActionService')

local jumping = false
local leftValue, rightValue = 0, 0

local function onLeft(actionName, inputState)
	if inputState == Enum.UserInputState.Begin then
		leftValue = 1
	elseif inputState == Enum.UserInputState.End then
		leftValue = 0
	end
end

local function onRight(actionName, inputState)
	if inputState == Enum.UserInputState.Begin then
		rightValue = 1
	elseif inputState == Enum.UserInputState.End then
		rightValue = 0
	end
end

local function onJump(actionName, inputState)
	if inputState == Enum.UserInputState.Begin then
		jumping = true
	elseif inputState == Enum.UserInputState.End then
		jumping = false
	end
end

local function onUpdate()
	if player.Character and player.Character:FindFirstChild('Humanoid') then
		if jumping then
			player.Character.Humanoid.Jump = true
		end
		local moveDirection = rightValue - leftValue
		player.Character.Humanoid:Move(Vector3.new(moveDirection,0,0), false)
	end
end

RunService:BindToRenderStep('Control', Enum.RenderPriority.Input.Value, onUpdate)

ContextActionService:BindAction('Left', onLeft, true, 'a', Enum.KeyCode.Left, Enum.KeyCode.DPadLeft)
ContextActionService:BindAction('Right', onRight, true, 'd', Enum.KeyCode.Right, Enum.KeyCode.DPadRight)
ContextActionService:BindAction('Jump', onJump, true, 'space', Enum.KeyCode.Space, Enum.KeyCode.Up, Enum.KeyCode.DPadUp, Enum.KeyCode.ButtonA)

So this controller only allows you the go left and right and jump. Because after all it is a 2D game, but I wanted to try something and I cant figure out how to script W and S to go foward and backwards.

You'll need to change these lines from:

ContextActionService:BindAction('Left', onLeft, true, 'a', Enum.KeyCode.Left, Enum.KeyCode.DPadLeft)
ContextActionService:BindAction('Right', onRight, true, 'd', Enum.KeyCode.Right, Enum.KeyCode.DPadRight)

To:

ContextActionService:BindAction('Left', onLeft, true, 'w', Enum.KeyCode.Left, Enum.KeyCode.DPadLeft)
ContextActionService:BindAction('Right', onRight, true, 's', Enum.KeyCode.Right, Enum.KeyCode.DPadRight)

We're just changing the keys from "a" and "d" to "w" and "s" these are lines 46-48 in your code.