I am new to After Effects and I was wondering how can I make this transition @0:40
This looks like the first clip is fading to white and then the second clip is fading from white to the original color.
You can achieve such a fade by using a levels or curves effect with two keyframes (one with the default value and one such that the image is very bright / almost everything white).
This tutorial shows how to use the curves effect:
And this one how to work with keyframes (you can keyframe the curves parameter as any other parameter):