You need to have administrator privileges or to be a Project Manager of a project to be able to copy a project.
To copy a project, click on the Project Settings icon (dotted menu) and select Copy Project.
Choose which information to be copied to the new project, e.g. the boards; all the tasks, the custom fields, you may choose whether to preserve the assignees or/and the links, etc. Once you make your choice -> click on the Copy Project button.