How can I clone and use the default taxonomy view to learn its behavior?
The % symbol in the URL works a placeholder for a parameter. So if you access taxonomy/term/1 or taxonomy/term/2 note that the number is actually the term id, so that is the way you "view" (access) the view. You can see, edit, add, delete or modify those parameters if you click the advanced option in the view and you will see the option "Contextual filters".

Now, to clone it, you can access the up right button and then click the "duplicate" option, wich for this case will have a URL /admin/structure/views/view/taxonomy_term/duplicate. Note that this will clone all the view and its styles, in this case, will duplicate a view with two styles: the page view and the RSS view.