How does namespace usage differ from library inclusion in a project?

In C#, namespace and using directive are different concepts, although closely related:

• Namespace — a logical grouping of classes, interfaces, and other types within the code. It helps organize code and avoid name conflicts.

• Using directive — a statement that allows using types from a specific namespace without needing to specify the full namespace path.

For example:

using System.Text; // importing the namespace

namespace MyApp {
    class Program {
        static void Main() {
            StringBuilder sb = new StringBuilder(); // without using, you'd have to write System.Text.StringBuilder
        }
    }
}

Thus, importing a library means adding a reference to an external assembly (DLL) to the project to use its code, while using is a way to simplify access to types within imported namespaces.