How do I import a module? I am working on Drupal 8 and I have migrated my Drupal 7 website to Drupal 8 using the Migrate Upgrade module, but none of the modules is imported from my previous Drupal 7 site.

How do I import modules from Drupal 7 to Drupal 8 without using Drush commands?  I'm not much familiar with Drush.

I have seen the article in which a process is given to import modules using  Drupal Module Upgrader, but it's based on Drush.

Is there any simple method to port Drupal 7 modules to Drupal 8?
Perhaps, your question in bold needs to be reworded to Is there any simple method to port D7 modules to D8? Which is what you're really after.

If you are referring to CUSTOM modules (not drupal.org contrib  modules) then the fastest / most simple way is to use Drupal Module Upgrader which you mentioned in your question. In module page they show you a video with all the steps. 

There is no reason to be afraid of Drush. As a Drupal newbie, Drush can seem scary/daunting, I used to avoid it too, but once you learn Drush, which is not hard, you will discover that is super useful and a time saver. You will wish you learned it earlier.

It is important to note that while the Drupal Module Upgrader will port/rewrite some of the code, some of the code may not (depends on how complex your module is) and you will have to manually modify/rewrite certain parts by hand.

Other than using Drupal Module Upgrader, there is no other choice, but to manually re-write your entire module.

If you are referring to Drupal.org Contrib Modules then you will need to download the D8 version, if there is one.