How to trigger a cutscene by touching a part?

###Player Events

The CharacterAdded event will automanically run whenever the player's Character is loaded into the game. This is why it is running when the player joins.

###Touched Event

Roblox has an event called Touched. This event will run whenever an object touches the part you set it to be. We can have this run for the part we want to be touched. It has one parameter, which is the object that touched the part. We will call this TouchPart.

When doing a Touched event, if you want an action to perform when a player touches it, you must check if the touchee is a player. Otherwise, your script will error.

###Solution

-- localscript in starterGui
local player = game.Players.LocalPlayer
local TweenService = game:GetService("TweenService")
local cam = workspace.CurrentCamera

local TouchPart = game.Workspace.Part -- Change this to the part you want to be touched

function play(char)

    local PP = char.PrimaryPart
    cam.CameraType = Enum.CameraType.Scriptable

    local BCFrame = PP.CFrame * CFrame.new(10,10,10) * CFrame.new(0,math.pi,0)
    local targetCFrame = PP.CFrame * CFrame.new(0, 0, -10) * CFrame.Angles(0, math.pi, 0)

    cam.CFrame = BCFrame 

    local tween = TweenService:Create(
        cam,
        TweenInfo.new(2),
        {CFrame = targetCFrame}
    )

    tween:Play()
    tween.Completed:Wait()
    cam.CameraType = Enum.CameraType.Custom
end

TouchPart.Touched:Connect(function(hit)
	if hit.Parent:FindFirstChild("Humanoid") then -- checking if the object that touched it is a player
		play(hit.Parent) -- plays the animation
	end
end)

-- This event below will run when the player is added. Delete it all if you do not want this!
player.CharacterAdded:Connect(function(character)
    wait(3)
    play(game.Players.LocalPlayer.Character)
end)