Short answers, pulled from the story.
The Hollywood Park Racetrack operated as a thoroughbred race course from 1938 until it shut down for racing and training in December 2013. Most of the complex was demolished in 2014 to make way for new construction with the rest demolished in late 2016 after the Hollywood Park Casino moved to a new building.
Stan Kroenke purchased a parcel of land just north of the former racetrack site on the 31st of January 2014 according to a Los Angeles Times report. This purchase set off immediate speculation about whether the Rams would return to their home of nearly fifty years.
SoFi Stadium features an independently supported translucent canopy covering the stadium proper, the adjacent pedestrian plaza, and the attached performance venue. The million-square-foot canopy is made up of 302 ETFE panels, 46 of which can be opened to provide ventilation.
The NFL approved the Inglewood proposal and the Rams' relocation back to Los Angeles 30, 2 on the 12th of January 2016 over the rival Carson proposal. Turner Construction and AECOM Hunt were announced on the 14th of July 2016 to oversee construction while HKS designed the stadium.
The St. Louis Rams were first to commit to moving to the stadium as NFL approval for their relocation to Los Angeles was obtained on the 12th of January 2016. Both teams contributed a $200 million stadium loan from the NFL and personal seat license fees to construction costs while paying $1 per year in rent to StadCo LA LLC.