Hi! Thanks for reading and for any kind of help you can give to me!

I don't know what the page ng-newsletter actually is, so everything I am going to say its just an opinion/question... I've seen some post on it and I even thought of getting the "free book", but when I try to sign up I can't find where. They also say about a newsletter in my email but again I can't find where to sign up. On the bottom of the page there are a few links, one with the text "ng-book", which sends you to a page where you can buy (not for free) a book. Also at the bottom the license is from fullstack.io, a page with a single image and a mail to contact them. All this looks so suspicious for me, but I'm not an expert since I'm just an student... Can anyone tell me how to get that free book if it actually exists? Or even sign up on the page if they are actually legit (I don't wan't to say bad things when I don't know about them, so I'm just asking)