The project calendar includes not only the final date that the project must be completed by, but also a detailed list of the steps and outcomes and their due dates needed to complete the project.
For example you are writing a report. You would need due dates for all of the steps of writing, planning, research, organizing, drafting, revising, and proofreading in addition to the due date for the report.
When you plan a project calendar there are two tips that make the project itself go smoother: 1) be as detailed as possible with the project calendar and 2) use backward planning. Backward planning simply means you start with the due date for the project and then work backwards through the calendar from that date ensuring that you have enough time to complete each of the steps that are needed to finish the project.
To return to the report example. If it is due March 2nd, then you would plan to work proofreading from Feb. 28 through Mar 2. You would spend from Feb. 18 to Feb. 28 revising, Feb. 14 through 17th drafting, Feb 13th organizing, Feb. 7th to Feb. 12 researching and you received the assignment on Feb. 6th and spent that night planning. This is just an example but you can see how backwards planning works.
For complex projects you may want to use a Gantt chart or project management software such as Asana, Microsoft Project, Clarizen, Wrike, DaPulse, and a host of others.