And so we reach the end of John! John, the author of the book (who else?), saw the events as listed in the book and wrote them down. But there are a lot of other things that Jesus did. In fact, John thought that if all the things that Jesus did were written down, then "even the world itself could not contain the books that would be written"! (21:25) Pretty incredible.
Some of Jesus's other actions were recorded in the other gospels -- Matthew, Mark, Luke. However, it's heavily implied that the list of things that Jesus did included the actions done while in heaven as well as all the testimonies about Jesus over the course of history. In other words, Jesus did a lot, and he would continue to do a lot. Even today!