Short answers, pulled from the story.
The song I Want to Hold Your Hand became the first Beatles track recorded with four-track machines in 1963. This new technology allowed engineers to build recordings layer by layer instead of capturing a live performance on two tracks.
Abbey Road marked a final technological transition as the only Beatles album recorded using the transistorized TG12345 mixing console. Earlier records relied on REDD valve consoles which had an aggressive edge that the newer transistorized console lacked.
I Feel Fine recorded on the 18th of October 1963 started with a feedback note produced by plucking the A-note on McCartney's bass guitar. George Harrison stated in The Beatles Anthology series that the effect began accidentally when a guitar sat on an amplifier before Lennon worked out how to achieve this live on stage.
The Beatles first used samples on Yellow Submarine added on the 1st of June 1966. Brass band solos constructed from Sousa marches were transferred to tape then cut into small segments and rearranged to form brief solos added directly to the song.
Geoff Emerick engineered Eleanor Rigby on the 28th of April 1966 using close-miking techniques where microphones almost touched the actual strings. Ringo's drums received similar treatment with a large sweater stuffed inside the bass drum to make it more prominent within the mix.