Baby showers (at least in my area) are done in the last part of a pregnancy. They’re used to give gifts and useful items to a new parent(s) to prepare for the coming of the child. (Baby clothes, diapers, stroller, etc.)
It’s also a party to celebrate the birthing parent (and more recently, the non-birthing parent) as a last hurrah before they’re tied up with new baby for months.
It’s also typically a bigger deal for the first child, and either omitted or toned down considerably for subsequent children.