RSS (Really Simple Syndication) is a database feature that broadcasts new content when it is added. By copying a related URL into an RSS reader app, a user can automatically see newly posted material without having to manually visit a database or search for it (many websites also offer RSS feeds - here, for example, are the ones available from the New York Times).
This short video provides an overview:
Alerts are a database feature that lets you be automatically informed, usually by email, when new material related to a particular author, publication, search, keyword, or subject has been added.
Alerts can save you from having to repeat searches if you're working on a project over time, or want to stay regularly updated about new material from a particular source, or about a specific topic.
Email alerts typically include a link to a new item, information about it, and, in some cases, its full text in the email itself.