There are three ways in which Logynon gives you protection from pregnancy.
The two hormones in it stop the ovaries from releasing an egg during ovulation, and thicken the mucus in the neck of the womb, which makes it more difficult for sperm to reach an egg.
They also make the lining of the uterus thinner, which reduces the chances of a fertilised egg latching on to the uterine wall, which it needs to do in order to grow.
The combined pill tends to make your periods lighter, regular and less sore, so there are additional benefits to taking it too.