I'm starting with BDD and this is my story:

Feature: Months and days to days
    In order to see months and days as days
    As a date conversion fan
    I need a webpage where users can enter
    days and months and convert them to days.

I have some doubts ...

Should I write my scenarios before coding anything or should I first write a scenario and then write code, write a scenario again and then write code, and so on ... ?

If I should write my scenarios before, can my steps be approved and production code still does not get done?

When should I do refactoring on my code? After the feature is done or after each scenario implementation?