What's the role of 'using' directives in resolving CS0246?

'using' directives tell the compiler where to look for classes and other types. If you're using a class from a specific namespace, you *must* include a 'using' statement at the top of your script. For example, `using System.Collections;` or `using UnityEngine;`. Without the correct 'using' statement, the compiler won't be able to find the class.