I'm working with AE, my problems are all related to "green screen".
(I wanna put different videos in each polaroid)
Thanks everyone for answering to my questions.
Each element is a separate layer. If you want a bunch of videos inside Polaroids there is no need to green screen, just make a comp the size and shape you want then use a solid layer with a mask or create a shape layer that looks like a Polaroid frame and put a video below it. No magic here, just layers. Now you create a comp the size of your final output (most of the time this is HD1080 29.97 in non PAL countries) and drop in all of your Polaroid + video layers. In the example you showed the layers are then all changed to 3D and their position is animated. A light is added to create the shadow.
You add sub titles by adding a text layer. After Effects is all about layers. You'll be better off if you start with the basics, learn the interface, and learn how to render. To get started start here: Basic Workflow.
One last point. After Effects is NOT for editing videos. It is designed for creating shots or short sequences. To edit you want to use Premiere Pro or some other NLE. An AE project longer than a few seconds for a newbie is a crazy undertaking.
Thanx for answering! Have a nice day!