A matter checklist is used to keep track of each specific task that needs to be done to intake a matter. It consists of the consultation, intake form, engagement letter, and any other custom tasks you choose to add.
When you create a matter, you can choose to add the Consultation, Intake Form, and Engagement Letter to the checklist. You can add as many other custom tasks to the checklist as you'd like.
Read this article about how to add a task to a matter for more details.