Hi,

  I think you are new to odoo .please go through this link https://www.odoo.com/documentation/12.0/ 

  when a new record creates a default method called create is called.we can super it if we want to make some changes on  the record while creating.

 if you are trying to extend the leave calendar model you can do it by using _inherit = 'model you want to change' and write the method you want to add.