scenario is: user can able to select the date and add an event by himself just like Messaging --> Calendar. i just want to know where this code is located. If i got that it will be more helpfull. Thanks

and i need how to implement that in my custom module.

I believe the code is located in crm (crm.calendar)? In order to implement it, you should most likely just inherit this module in your custom module and allow people to create crm.calendar objects from a specific view. The calendar is a mere view-option, like list, kanban and form. Look in the XML for tags and you will see how that is constructed.

ok thanks a lot Ludo