Short answers, pulled from the story.
The Navy transferred the former Banana River Naval Air Station to the Air Force in 1948. This site on the East Florida coast offered launches over the ocean away from populated areas.
Each Mobile Launcher weighed 6 million pounds and stood 40 feet tall. The umbilical tower contained nine retractable swing arms extending to provide access for people wiring and plumbing.
SpaceX signed the 20-year lease modifying the pad for Falcon 9 and Falcon Heavy launches on the 14th of April 2014. Modifications included constructing Horizontal Integration Facilities similar to Cape Canaveral facilities.
The Space Launch System launched from Complex 39B on the 16th of November 2022 at 06:47:44 UTC. This marked return of human spaceflight to the Moon after decades.
Kennedy Space Center director Robert D. Cabana cut the ribbon on the 17th of July 2015 marking completion. The concrete pad measured 60 feet wide by 100 feet long supporting combined weights up to 1 million pounds.