The mini pill is a progesterone only pill. It is known as the mini pill as it only contains one hormone, whereas other contraceptive pills, known as the combined pill, contain both progesterone and oestrogen.
The mini pill has the same function as combined pills. By taking the mini pill, you are preventing pregnancy as it thickens mucus in and around the womb. Thick mucus decreases the chance for sperm to reach the egg, and also for the egg to implant and develop.