How can I make someone a Project manager?

Go to the Projects page and select Edit project (from the Actions drop-down menu).

Then go to Add People & Permissions. After you add members by clicking on the plus (+) button, You should see an option for Manage Project permissions.

After you permit to Manage a Project to an employee, he/she will become the Project manager for that project and will be able to change the details of that project.

With permission to view reports, Project managers can check the reports for the project.