Many people were baptised (christened) as a baby but have had little contact with the Church since. Baptism is, nevertheless, permanent and cannot be cancelled or repeated. So, if you were baptised as a baby, in whatever church that took place, you are still baptised and you cannot be baptised again.
Some people do not know whether they have been baptised or not. It is important to find out from parents or older relatives and to discover where it took place, because you may need to obtain a baptismal certificate.