1-there is a registered user (author). 2 - he enters the site under his login. How can he create a new article ? This is possible without going to the admin panel? By default he is the author of the account may only change the published materials.
Yes, it's possible probably since Joomla 1.5
This is a basic Joomla knowledge, no relation with JoomShaper products.
Just add Menu item Create Article. Whole rest depends on Joomla ACL settings only.