Force new articles to have tags (term + subterm) associated with it previous question

I have a site where articles need to be classified as, apple, banana, cranberry, etc....

Each category has sub-cats like apple - 1, apple - 2, ... banana - 1, banana - 2 ...

Now apples can have 10 subs and banana can have 200 or something like that.

I already make a vocabulary using taxonomy of all the terms and subterms.

What I need to do is have it so that users submit articles and it must have a category and sub-cat associated with it.

I want to do it this way so that I can have an index page of all apple articles, or just apple - 1, or banana - 2's ... etc.
What you are seeking to do is very basic and one of the early things you learn how to do in Drupal.  The simplest way to answer your question is to recommend you get a book such as Drupal 7 by Tom Geller or any of the other introductory Drupal books. Lynda.com also has a video series that can fill you in on how to use Drupal.  You can accomplish want you seek by modifying or creating a content type and adding field s linked to taxonomy terms. You can make it a requirement to add a value for each new entry.  Eventually you will want to master the Views module to find your content and display it.

Before you start working on the design of a site, yuo may want to spend some time studing Drupal basics. Drupal has a steep learning curve in the beginning and you will have to cover a lot of ground before it starts clicking and you will feel confident diving into a project.