Why i can use a book where i didnt buy??

Why i can use a book i didnt buy? 
It says the content is currently shared throught a active campain?

when the campain is over can i still see the books?

Warum kann ich ein Buch verwenden, das ich nicht gekauft habe? 
Es heißt, dass der Inhalt derzeit über eine aktive Kampagne geteilt wird?

Wenn die Kampagne vorbei ist, kann ich die Bücher noch sehen?

Quote from CociBaeretatze >>

Why i can use a book i didnt buy? 
It says the content is currently shared throught a active campain?

when the campain is over can i still see the books?

 When you are in a campaign, and a member of that campaign has a Master subscription, the books can be shared with all the members. 

When you leave the campaign, you loose access to those shared books.