Installation and setup of the Emulsify CLI itself is documented thoroughly in its GitHub repo.
How to use the CLI in a typical workflow is documented in the Usage section of these docs.
Watch this video to get a quick walkthrough of the CLI in action!
emulsify initallows developers to easily create an Emulsify project. it attempts to detect the platform being used, and implements the appropriate starter (such as emulsify-drupal).
emulsify component listwill return a list of components available within the system selected for the project.
emulsify component installwill fetch a specific component into the project.
Details on the commands above, and other features/options are documented in the repo, so please take a look there.