Usages of эта
Эта книга самая интересная.
This book is the most interesting.
Эта книга полезная.
This book is useful.
Эта статья довольно длинная, но я прочитал её почти до конца.
This article is quite long, but I read it almost to the end.
Elon.io is an online learning platform
We have an entire course teaching Russian grammar and vocabulary.