How to create a fade in-out transition effect (gui), if a player touches a part?

Simply take a black image, place it over the entire screen, set it to be invisible, and slowly decrement its transparency when you want to fade-in, or slowly increment it when you want to fade-out.

Instructions:

1. Insert a ScreenGui into the StarterGui if there isn't already one there.

2. Insert a ImageLabel into the ScreenGui.

3. Change the dimensions of the ImageLabel until it covers the entire screen.

4. Set the BackgroundTransparency of the ImageLabel to one.

5. Insert a blank localscript into the ImageLabel and paste the code below into it.

        FADE_SPEED = 1;
        function FadeIn()
        while (script.Parent.ImageTransparency < 1) do
            script.Parent.ImageTransparency = script.Parent.ImageTransparency + FADE_SPEED/30;
            wait(FADE_SPEED/30);
        end
    end
   
    function FadeOut()
        while (script.Parent.ImageTransparency > 0) do
            script.Parent.ImageTransparency = 	script.Parent.ImageTransparency - FADE_SPEED/30;
            wait(FADE_SPEED/30);
        end
    end
   
    wait(3);
    FadeIn();
    wait(3);
    FadeOut();