When you install the Checklist app, two new custom field types become available in your installation:
Checklist: Contains all the nitty-gritty you need to start using Checklist.
Checklist Read-Only Proxy: Renders the Checklist field in different visual formats, such as a banner or progress bar, which is very useful on Agile cards.
Before you can start integrating checklists into your workflow, you first need to add a Checklist custom field to Jira and configure it to suit your needs.
To get started, proceed to https://okapya.atlassian.net/wiki/spaces/CHKDOC5/pages/1951596558/Adding+a+Checklist+custom+field.
SERVER documentation (On Cloud? Go here.)