Does anyone know how to make a hold shift to run script? and when u stop holding down sprint stops?

Attention to any mods, if I'm breaking any rules please let me know - I will take my answer down.

So, I'm going to use many comments to explain what's happening so this person can learn.

Read this script - the comments too, hope this helps..

print("Sprint Script Loaded")
-- You must put this in a local script because it's handling user input
-- This script should go in StarterPlayer > StarterCharacterScripts

-- We can only access LocalPlayer in a LocalScript it cannot be accessed in a server script nor ModuleScript

player = game.Players.LocalPlayer

mouse = player:GetMouse() -- This is what will be detecting if you pressed a key

 -- Here we create a function with a parameter 'key' key is the key that was pressed

local function onKeyDown(key)
-- This checks to see if the key code is the same as shift
if string.byte(key) == 48 then -- 48 is the keycode to shift 
player.Character.Humanoid.WalkSpeed = 29 -- This is changing the persons walkspeed
end
end

local function onKeyUp(key) -- a function going to be fired when a key is released
if string.byte(key) == 48 then -- Again here we check to see if it's the shift key
player.Character.Humanoid.WalkSpeed = 16 -- Here we are changing the walkspeed back to default which is 16
end
end

-- Here we are connecting the two functions to the 'KeyDown' and 'KeyUp' events.

mouse.KeyDown:connect(onKeyDown)
mouse.KeyUp:connect(onKeyUp)