The list of milestones for a given project is set by you when creating your schedule. While you can have any number of levels of tasks and subtasks, the top level of tasks will set your project's milestones. You decide how many milestones, what they should be, and how many tasks should fall under each milestone category.
Click the "Collapse All" button at the top of the Gantt or Task View to view the list of your project's milestones.
This list is prominently displayed on the clients’ dashboard, with check marks to indicate when the work has been completed (when all of the subtasks are 100% complete). The last milestone and next milestones are also referenced in the summary e-mails to your clients.
If you are sharing the project's schedule (either the calendar or the Gantt view) with your clients, they will see the completion percentage for each milestone, along with the anticipated finish date.
Otherwise, if you have not shared the schedule, your clients will still see the list of milestones, with check marks to indicate work that has been completed, or full circles to indicate work that has started. Your clients will not see percentages or anticipated finish dates if the schedule has not been shared with them.