You will be creating many projects in this course, and it is always best to think of each project as a separate endeavour. Sometimes, a novice programmer may finish Project 1, but rather than starting a new project, will instead just try to modify a previous project.
Instead, each time you want to start a new project, be it for a course project, for experimenting with source code from class, or working on a side project, create a new project in Eclipse. This is described in much greater detail on the Eclipse page, but in summary it includes:
You can now add source files by selecting File→New→Source File.
You can always select the project you want to work on by clicking on the project name in either the Project Explorer tab or the more specific C/C++ Projects tab. If you cannot see either tab for this in the left panel, you can make either visible by selecting Window→Show View→Project Explorer or Window→Show View→C/C++ Projects.
The state of a project is either open ( where the "C" indicates it is a C/C++ project) or closed (). You can toggle between these two states by selecting the project in the Project Explorer and then selecting either Project→Open Project or Project→Close Project. Alternatively, you can toggle the state of a project by right-clicking on the project and selecting either Open Project or Close Project, whichever is on the context-sensitive menu that appears.
It is highly recommend to have at most one project open at a time.