From a Google Scholar Blog Post:
We analyze your articles (as identified in your Scholar profile), scan the entire web looking for new articles relevant to your research, and then show you the most relevant articles when you visit Scholar. We determine relevance using a statistical model that incorporates what your work is about, the citation graph between articles, the fact that interests can change over time, and the authors you work with and cite. You don’t need to configure updates or enter any queries. We’ll notify you about new updates by displaying a preview on the homepage and highlighting a bell icon on search results pages.
If you don’t have a Google Scholar profile info and links about how to create one are available here. The blog post says your profile must be public to receive article suggestions. By default, profiles are private.