How do I script a run/walk with the shift key?

I would like to say, before I do this, that this is not a request site. I will help you out because You may not have read or understood that. In return though, I would like you to read and analyze the script, so you never have to ask this again. Thank You

Here is the script.

InputService = game:GetService("UserInputService") -- Sets a var to UserInputService
local plr = game.Players.LocalPlayer -- Sets Player
plr.CharacterAdded:Wait() -- Waits Until Player's Character has loaded in
plr.Character:WaitForChild("Humanoid") -- Waits Until Character's Child Humanoid Loads
local char = plr.Character -- sets a Variable to the player's character.
local hum = char.Humanoid -- Sets a Variable to  Humanoid


InputService.InputBegan:Connect(function() -- Function for Input being given
    local actionKey = Enum.KeyCode.LeftShift -- sets variable actionKey to LeftShift
    local keysPressed = InputService:GetKeysPressed() -- sets Variable to a table of keys pressed
    for _, key in ipairs(keysPressed) do -- set a loop to check for all keys pressed
        if (key.KeyCode == actionKey) then -- checks If the key pressed is LeftShift
            hum.WalkSpeed = 20 -- You can change these how you want
            wait() 
            InputService.InputEnded:Connect(function() -- Function for InputEnded
                hum.WalkSpeed = 16 -- Sixteen is the default walkspeed
            end)

        end 
    end
end)

Additional Notes-

-You must use a Local Script and put It in StarterPlayerScripts.

-Try to mess with It and make something cool out of it

-Please don't request Code on this site, and Instead request help with your code.

-Have Fun