A christening is a naming ceremony, the baptism is the emersion in water part. Catholics do baptisms, they don't do christenings. But other christian faiths like orthodox do Christenings where the child is also given their name at the baptism.
Does that make sense?
Catholics will call it a Baptism and my friend who's orthodox call it a Christening, it's the same thing (baptism part) but then the orthodox also name their child officially in the church (it must be a saints name)