A good reminder, primer
This is a good starting place for a new believer, or a not so new believer in Jesus Christ, on what the basics of the Christian beliefs are. Surgeon's Catechism is more modern, has pretty much the same contents, with one major difference: infant baptism and how baptism is performed. Surgeon indicates infants are not baptized, whilst Westminster says they are. While an interesting difference, it should not cause either of these catechism to be discarded. Both are full of similar to same information, what they agree on are the most important issues. For those wishing an infant baptism explanation, it has to do with the idea of a infant being protected from hellfire should it die before it grows enough to accept Jesus. Both sides of this would assent to God being gracious to infants who are not yet old enough to understand biblical teaching. Surgeon just wanted folks to know that being baptized as an infant did not invalidate a person from needing to personally accept God's word and become a Christian when they were old enough to understand. Historically, Westminster is two hundred years older and closer to the Reformation, when being split of from Catholicism was a fresher concept.