In a multi-chapter fan fiction, there ought to be a box in the top right corner which says "1. Chapter 1" or whatever the first chapter's title is if it's been titled. You simply need to click on that box, open the drop down list and select the next chapter. Or you can click the Next button which is to the right of the drop down box.
If you're talking about fanfiction as articles on Fanpop, not fanfiction.net, the simple answer is that you can't. There's no way to connect different chapters. You just have to look at the articles in the club, or in the member's activity feed, and open up the next chapter article. That's why Fanpop's fanfiction articles work best for oneshots and not multi-chapter stories.
posted over a year ago
Answer edited because I realised the question could be asking about fanfiction on Fanpop.