Hi! Im trying to make a sprint script there players need to press Shift to sprint?

Something like this would work, but you should re-edit your question and give code.

--in a local script
--in startercharacterscripts
local userInputService = game:GetService("UserInputService")
local character = script.Parent
local humanoid = character:WaitForChild("Humanoid")
--get the speeds
loca RUNSPEED = 25
local DEFAULTSPEED = humanoid.WalkSpeed

--if they press shift
userInputService.InputBegan:Connect(function(keyPressed)
    if keyPressd.KeyCode = Enum.KeyCode.LeftShift then
        humanoid.WalkSpeed =  RUNSPEED
    end
end)

--when they let go of shift
userInputService.InputEnded:Connect(function(keyPressed)
    if keyPressed.KeyCode = Enum.KeyCode.LeftShift then
        humanoid.WalkSpeed = DEFAULTSPEED
    end
end)

So it seems you want to make a sprinting script ey? well I'll help you out. P.S. Im not too sure on how to make it work when you hold it down, So im doing my best.

now First you create two local scripts and put them into StarterPlayer>StarterCharacterScripts.

Now, Name the first one anything you like and name the second one anything too. (But I don't recommend putting spaces in the Name)

Now you put the second script onto the First one making the Second local script the child of the first one.

This is the First Scripts code.

local UIS = game:GetService("UserInputService")
local WalkSpeed = game.Players.LocalPlayer.Character.Humanoid.WalkSpeed
local SecondScript = script.(Second Script Name)

UIS.InputBegan:Connect(function(input)
    local Pressed = input.KeyCode
    if Pressed == Enum.KeyCode.LeftShift then
        WalkSpeed = 30 --Add any number on what speed you want.
        script.Disabled = true
        SecondScript.Disabled = false
    end
end)

And this one is the Second script code.

local UIS = game:GetService("UserInputService")
local WalkSpeed = game.Players.LocalPlayer.Character.Humanoid.WalkSpeed
local FirstScript = script.Parent

UIS.InputBegan:Connect(function(input)
    local Pressed = input.KeyCode
    if Pressed == Enum.KeyCode.LeftShift then
        WalkSpeed = 30 --Speed number thing.
        script.Disabled = true
        FirstScript.Disabled = false
    end
end)

You can just copy and paste the scripts above.

Hope that this works for you. Toodles.

(They have to be LocalScripts and/or in StarterPlayer>StarterCharacterScripts, else this would not work)