All users with either Admin, Author or view-rights can see the check-list and Milestones, but only Admins can modify the items.
The check-list is a pre-defined list of items, a non-comprehensive list of steps in a guideline process. It follows the AGREE II requirements and the steps used in SNAP-IT
The milestone feature lets you create your own milestones, assign a date and a person responsible for it.
There is a much more comprehensive Checklist available from McMaster that you also might want to check out.