At what point in a project do you sand/finish/paint?

I’m looking forward to starting my very first woodworking project! I’m planning on making this end table.

https://www.ana-white.com/woodworking-projects/farmhouse-side-table

I’m unsure, however, when I should sand and stain or paint it. Once it is completely put together (seems difficult to get all the nooks and crannies and have a finished looking piece)? Or once all the cuts are done but before assembling?