The purpose of the Shorter Catechism is to educate lay persons in matters of doctrine and belief.
The catechism is composed of 107 questions and answers. The first 12 questions concern God as Creator. Questions 13-20 deal with original sin and the fallen state of man's nature. Questions 21-38 concern Christ the Redeemer and the benefits that flow from redemption. The next set of questions, 39-84, discuss the ten commandments. Questions 85-97 teach concerning the Sacraments of Baptism and Holy Communion. The final set of questions 98-107 teach and explain the Lord's prayer.
( taken from http://en.wikipedia.org/wiki/Westminster_Shorter_Catechism )