A solution can contain multiple projects. Working with multiple projects is not much different than working with a single project. Use the Solution Explorer to navigate between the projects in the current solution.
You might add a project to a solution to copy code between projects. You might want to reference the procedures, functions and classes in one project and use them in another project. By adding multiple projects to a single solution, it allows you to use a project as a set of common utilities that you might use with more than one project.
Unload a project from a solution
Projects can be unloaded from a solution when they are no longer needed. If you no longer want a project to load with a solution, you can unload the project and then reference the compiled DLL assembly of the project instead. Working with the compiled DLL helps to prevent accidental edits to the source code.