Lexis is a licensed database with federal and state case law with extensive coverage.
You generally want to turn to Lexis for case law after you have already surveyed secondary sources on your topic and after using free online sources for case law such as Google Scholar and/or used print digests.
There are four main ways to find case law:
Terms and connectors: From the homepage, you can select filters by the main search box or "Browse" to reach a particular database. For a reminder of Lexis terms and connectors, click "Help" from the "More" dropdown menu in the upper right.
By subject: From the homepage, click "Browse." You can browse the lists of Sources and Topics and drill down from there or you can do a keyword search within the lists.
Lexis has no print equivalent for its subject arrangement of cases akin to West's digest system.
Finding tools within an individual case:
Lexis is more comprehensive and sophisticated than free online resources.
This is an expensive resource. You should be aware of how your firm or employer is charged for its use. Using it cost effectively within that framework requires thought and training on how best to use the database. Lexis is newer than West, and thus does not have a print equivalent to West's digest system.