Imagine that you had 50 pages that all need whatTimeIsIt(), findDayOfWeek(), DateTime, and Tomorrow. You wouldn't want 50 different copies of these functions and variables. No, you would rather have a single copy of these items so that you could manipulate the single copy and execute your updates to all 50 pages at once.
Now you know how to do that.
Moving Forward:
This concludes Section 03. Next up Server and Error objects in Section 04.