You haven't really asked a question. But i'll assume that you want to know what a base and sub-theme is in drupal.

##**TLDR version**

A drupal subtheme inherits the template files (*.tpl.php) and assets (javascript, css, images) of the base theme. If you need to modify or change the template files. 

###**More on subthemes**


I think your best bet is to google it. I googled, "drupal subtheme" and found you  [drupal documentation regarding subthemes][1]:

> Sub-themes are just like any other theme, with one difference: They
> inherit the parent theme's resources. There are no limits on the
> chaining capabilities connecting sub-themes to their parents. A
> sub-theme can be a child of another sub-theme, and it can be branched
> and organized however you see fit. This is what gives sub-themes great
> potential.

Source: [Creating a sub-theme (drupal.org)][2]

In addition to the node page, if you're more inclined to watch a video this is probably a good bet: [Drupal Subthemes (youtube.com)][3]


###**Best Practices with subthemes:**
* Copy files from the base theme or use the drush command (when available)
* Utilize subtheme theme hooks to override your theme


  [1]: http://drupal.org/node/225125
  [2]: http://drupal.org/node/225125
  [3]: http://www.youtube.com/watch?v=R0i5P3QGm5s