How did George Harrison join The Beatles?
The third part of the equation that would become the Beatles fell into place on Feb. 6, 1958. George Harrison joined the Quarry Men, the John Lennon-led group that Paul McCartney had joined as a second guitarist and singer the previous summer.
Harrison, who was a few weeks shy of his 15th birthday, had known McCartney for about a year. The two were students at the Liverpool Institute and frequently took the same bus to and from school. A friendship blossomed, and the two began jamming together, even after McCartney had moved from Speke to Allerton.
When the Quarry Men – named after the Quarry Bank High School where the band was formed three years earlier – were looking to bring in a third guitarist (they had the idea long before Lynyrd Skynyrd), McCartney suggested his friend. The audition took place, strangely enough, on the top of a double-decker bus. At McCartney's prompt, Harrison took out his guitar and played Bill Justis' R&B instrumental "Raunchy," a No. 2 hit on Sun Records in 1957.
Source: ultimateclassicrock.com