How to create a Category Article listing with subcategories? I am new to drupal 7 and I want following page:

  Main Category

  (1) Subcategory1
    - post1
      Details
    - post 2
      Details
  (2) Subcategory2
    - post1
      Details
    - post 2
      Details


How can I do that? I think I can use Views but I need some further details.
Drupal Taxonomy is used to Categorize Content... Please have a look @ detailed tutorial here how to use taxonomy concept in Drupal to create categories and tag contents with categories.

You need to use views module to display the content by category.

Hope it helps.