Proliferation refers to rapid cell division creating billions of neurons Neurogenesis refers to the birth of new neurons
This is when the brain generates most of the neurons you'll have for life.
Looking at the early cells that form we first start with a bunch of Neuroepithelial Cells, which split off asymmetrically into Radial Glial and Neurons.
Theres also another form of division which is Differentiative Division which create Basal Progenitors whose sole purpose is to split into two neurons (just makes neuronal proliferation faster)
This process of Differentiative Division is also related to Differentiation and Synaptogenesis. Shortly after Proliferation and Neurogenesis starts, some neurons begin Migration neurodevelopment