Hi Abhishek,

for this you need to use inbound email action.

User has to send an email to the instance email address i.e. instanceName@service-now.com

Out of the box there are many inbound actions for Case table per COE

For example:

Name: Create HR Case

URL: https://instanceName.service-now.com/nav_to.do?uri=sysevent_in_email_action.do?sys_id=3a5370019f22120047a2d126c42e7063

You can refer those: OOB

1) type inbound actions in left nav

2) search with table contains hr_core

Regards
Ankur