Build an early-stage startup

I'm sure a lot of the content here is helpful to people, but I can't help the strong feeling of irony that a company the size of a small city is delivering a course on startups.

(Microsoft is a fine place, with multiple billion-dollar businesses, and is more successful than the wildest dreams of most founders, but a startup it is not)

Where can I find out how to build a late-stage startup?

What are some of the ways to conduct interviews for idea validation?