What is the difference between combined pill and progesterone only pill?

The combined pill as a type of pill that contains two hormones, estrogen and progesterone. The estrogen serves to give a withdrawal bleed. Normally this type of pill contains a one week break using placebo pills. Progesterone only pills are a contraceptive pill which are suitable for those women who are unable to take estrogen, or where is estrogen is contraindicated.