Short answers, pulled from the story.
Paul McCartney began shaping the melody for Get Back on the 7th of January 1969 during unstructured jamming sessions at Twickenham Studios. He played his Höfner bass while developing the primary riff that would become the song's backbone.
Billy Preston joined The Beatles on keyboards on the 22nd of January 1969 after arriving in England for television appearances. The group recorded about ten takes of the song on the 23rd of January using Preston's Fender Rhodes electric piano.
The Beatles performed Get Back three times during their rooftop concert on the roof of Apple Studios in Savile Row London on the 30th of January 1969. Police interrupted the group after receiving complaints from nearby office workers but the performance remains available on Anthology 3.
Apple Records released Get Back as a single on the 11th of April 1969 paired with Don't Let Me Down on the B-side. The single entered the UK charts at number one on the 23rd of April holding that position for six weeks.
The single credited The Beatles with Billy Preston making it the only Beatles release to include another artist's name. A chamber reverb effect runs throughout the single version which includes a coda after a false ending.