Short answers, pulled from the story.
"Here Today" is a tribute McCartney wrote to his friendship with John Lennon, who was murdered in 1980. McCartney composed it as an imaginary conversation the two might have had, capturing his grief and the things left unsaid between them.
McCartney wrote "Here Today" in mid-1981, less than a year after John Lennon's murder. He recorded it sometime after June 1981 at his High Park home studio in Campbeltown, Scotland.
George Martin, the Beatles' former producer, produced "Here Today" and arranged its string accompaniment. The string quartet recorded their parts at AIR Studios in London on the 30th of November 1981.
"Here Today" appears on McCartney's 1982 album Tug of War. Although it was not released as a single, it reached No. 46 on the Billboard Mainstream Rock charts.
One verse in "Here Today" refers to a night during the Beatles' first full American tour in 1964, when the group was stranded in Key West, Florida during a hurricane. McCartney has described how he and Lennon stayed up late and, in a rare moment, expressed how much they cared for each other.
McCartney regularly performs "Here Today" live and has said the song still moves him to tears at least once per tour. The song is featured on the live albums Back in the World, Back in the U.S., Amoeba Gig, and Good Evening New York City.