Drupal gives you the ability to re-use fields. If you have an "Image" field, you could choose to use that same field on every content type on your site. However, it's not always clear whether re-using fields is a good idea. Sometimes it is, sometimes it isn't.
It is recommended to create new fields, rather than reusing existing ones, unless you have a clear reason to do so.
Advantage: re-using fields can make your simpler and some content works well with re-used fields
Overview of the process:
Step 1: Instantiate the master site
In this example, we install Drupal with the following steps:
When a request for a page is sent by a browser , this request is received by the server hosting a drupal site. Suppose a request is sent for the page http://drupal.org/user/1 this request is received by drupal installation directory as URL user/1.
We have an .htaccess file inside drupal installation directory which is read on every request.