On drupal main page menu, number after /node/7/1 i am starting to learn drupal right now. I downloaded a template and I am trying to figure out where are all the components are stored. 

I encountered a problem where on the menu for website,  there are different submenu items under that menu. and one of the items has URL like this: www.example.com/node/7/1, another item URL like this: www.example.com/node/7/2, the list goes on, like www.example.com/node/7/3. When I click on any of those link, it brings me to the same page, however the representation is different. 

I am able to find node 7 in the content, however i am not able to find how to configure the number after /node/7. Can somebody tell me what does that number means? Thank you very much and have a great day.
Not sure I fully understand the question, but my 2 cents.

First, default Drupal URLs take the format of /{entity}/{id}/{action}, eg. /node/7/edit and /node/7/view. In both cases you are looking at the 7th node to be created, the first is the edit (admin) display, the second is the default display that visitors will see (view is dropped so you only see /node/7.

The second argument in your example is a little tricky as numbers don't give much away, so without knowing every module you have installed I would assume this is related to your template.

You can tell if this is the case by changing template to the default.

If these are the result of the custom template, the have a look in template.php as this is where theme level custom logic is done. On the off chance it hasn't been done well, have a look in the page.tpl.php and node.tpl.php files too.