1. Is it necessary to install JetPack? For what?
2. How can i create the “native wp” collage galleries you show on the demo?
3. the suscribe to posts widget is it from mailchimp?
4. Where can I put some custom CSS?
1. It is not absolutely necessary to install JetPack, however I recommend it. One of the things JetPack powers in this theme is the metadata for Facebook (Open Graph tags). So with JetPack installed, when you post links to your site on Facebook, it will display proper name, text and featured image (if post has it). Also, the subscribe form you see in the footer of the website in the demo is powered by JetPack. Overall, I’d recommend installing it.