Is it possible that every new article on the first (main.php) page has a short description such as, for example, articles in the Tatiana theme?

Yes, you have to modify loop-single.php, loop-single-premium.php and your style.css

Tnx ! Can you specify which part of the loop-single.php code should be edited?

Sorry, I found where I need it: just below the code

"<a class =" title "href =" <? Php echo osc_item_url (); ?> "> <? php echo osc_highlight (osc_item_title (), 100);?> </a>"

enter code for a short description! Thank you !!!

Do I need to insert some custom code in style.css to affect the _desc?