Different run and walk animations? [closed]

For the walking animation you could use roblox's default animation script and changing the animation Id.

For making it so that when the player presses shift you would play a running animation you could use the UserInputService to detect their input.

https://developer.roblox.com/en-us/api-reference/event/UserInputService/InputBegan

https://developer.roblox.com/en-us/api-reference/class/AnimationTrack

--Something along the lines of this in a local script because UserInputService only works on the client

local UserInputService = game:GetService("UserInputService")
local player = game.Players.LocalPlayer
local character = player.Character or player.CharacterAdded:Wait()

UserInputService.InputBegan:Connect(function(key, gameProccessed)
    if gameProccessed == false then
        if key.UserInputType == Enum.UserInputType.Keyboard then
            if key.KeyCode = Enum.KeyCode.LeftShift then
                local animation = Instance.new("Animation")
                animation.AnimationId = "the asset id of the animation"
                local runningAnimation = character:WaitForChild("Humanoid"):LoadAnimation(animation)
                runningAnimation:Play()
                character.Humanoid.WalkSpeed = "how fast you want them to run"
                --If you wanted them to stay running while shift is held down
                --[[while UserInputService:IsKeyDown(Enum.KeyCode.LeftShift) do
                    runningAnimation:Play()
                    wait(Length of running animation)
                end]]
            end
        end
    end
end)

You need to copy Animator from your character and put him in StarterCharacterScripts and then change animations there (in file and in script) to rbxassetid://YourAnimationId