Projects can grow to pretty big units over time. To keep an overview, you should split them in to smaller pieces, which are more easy to handle. At this point, modules can get pretty handy. They are exactly made for this situation and are like small projects in your projects. Milestones can hold ideas, items, votes, tasks, impacts and other modules. Since they are recursive, your projects can reach nearly infinity depth.
Open the project detail view or module detail view for creation. Click on the "+" in the upper right corner of the module box. A new view will appear and you'll have to input a name for the project you want to create. By clicking on the button on the bottom, the view will lead to its detail view.
Click the edit button in the details view of the module you want to edit. It will display a new view, which lets you change specific data for this instance or turn back to old versions.
Module deletion is possible by clicking the little bin button in the edit view of the instance to delete. By deleting a module, all of it's child objects will also be deleted. Deleting is just possible, if you own the module or got the change permission.