The book of Revelation was written by the apostle John. It relates prophesy in a chronological way. These prophetic events are also mentioned in the old testament, but not in chronological order. Therefore, the book of revelation, as its name implies, reveals to us what is to happen in the future.  

At a glance, the vision related by the apostle John is mainly of a  scroll (that is the way books were written in the time of John) that is sealed with seven seals.