Hello Raghav,
Please check the link below, it will help you understand this.
http://www.preact.co.uk/preact_blog/microsoft-dynamics-crm-automatic-case-creation
Please note that in CRM 2015, "Automatic Case Creation Rules" has been renamed to "Automatic Record creation and update rules"
Also in case you want to create cases from emails from unresolved senders, please ensure that in persobal settings under email tab "Automatically create records in Microsoft Dynamics CRM" is checked for creating contacts.
Hope it helps!
Regards, Abhishek Bakshi If you find this post helpful then please Vote as Helpful and Mark As Answer. Check my blog on https://mydynamicscrmblog.wordpress.com/