Scopus is a deep interdisciplinary database. We do not currently subscribe to it, for several reasons, but there are aspects of it that you may use for free, including their journal rankings, where you've been cited in journals they index if you create a profile, and so on.
The journals included in Scopus are significantly but not solely from the publisher Elsevier. They have a committee that judges which publications can be covered in the database. It also indexes some conference proceedings and some books.
The publications that they index change over time, as research emphases and publications change. It is fairly easy to discover what's being indexed in a given year, but relatively difficult to see the whole list of thousands of journals, plus or minus.
Registering in Scopus allows you to create a Scopus profile under your login, which allows you to track your citations in Scopus. This is not all of your citations, but just citations to content indexed in Scopus.