Where can I see the designed documents by the users?

You can keep track of everything previously created by the group of users by navigating to the 'My Documents' page. You can find this page by clicking on your name in the right top corner on the front end of the portal. Then click on 'My Account' and click on 'My Documents'. 

As an admin user, you can see all the documents created by the users. A user can either see all the documents, the documents created within the same group of users, or just his own documents. This is a setting that can be adjusted in the admin. Go to 'Pages' → 'My Documents' → Module: 'Outliner' and adjust the 'Visible documents'-dropdown here.