What About The Saddle Of Taking Contraceptives In The Mid

What about the saddle of taking contraceptives in the mid cycle...? I mean if a women start taking contraceptive in the mod of her cycle what will happen to the cycle?is the periods will come on it time or iy will be delayed until the pills are finished? Or if the it comes on its time then what the women should do during the periods.. To take the pills regularly or leave it... And should she start a new pack at the first day of a new cycle?