The application calendar begins from roughly Sept 15 and goes up to Jan for filing applications. However the exact the dates would depend on the college you are planning to take up.
Here is a list of year schools and tentative deadlines.
How to Apply?
You need to write the essays detailing your application as per school's requirement. Some schools want you to write 3 essays like ISB, some maybe 1 like Harvard and some may require you write to as many as 7-8 essays like INSEAD. You need to spend time researching your application and then it would take 20-25 days writing essays refining them.
Post that you need log on to application portal of every school and submit the application.
In case of any further questions, please feel free to ask.