There are 3 methods:
Start day 1 of your period (first day start)
Start the first Sunday after your period started (first Sunday start)
Just start it (quick start). This is less common and can confuse your body.
Whatever way you use, consider the first 7 days as fertile days and avoid unprotected sex.
The ideal is to wait for the first day or first Sunday start. Remember to read the patient insert that came with it.
Take care!