How to deploy software every second?
The "how" of extremely high-frequency deployment is all about very mature engineering practices and tooling.  The "unicorns" (Gene Kim's term for the type of company you list) have some of the best talent in the industry, and invest in the best technology.

One of several key practical differences between these unicorns and most other orgs is the level of automation they employ.  It is very difficult to automate the quality checks needed to maintain a constant flow of work from DEV, through testing environments, to Production.  Development and Operations must maintain high service levels internally.  Ops must provide self-service resources so developers aren't waiting on tickets to get new infrastructure.