Short answers, pulled from the story.
The Yellow Submarine album was made to fulfill the Beatles' three-picture deal with United Artists. The band disliked their previous film Help! and agreed to an animated film to reduce their involvement, accepting a contractual requirement to supply four new songs.
Apple Records released Yellow Submarine on the 13th of January 1969 in the United States and on the 17th of January 1969 in the United Kingdom. It came out two months after the Beatles' self-titled double album, commonly called the White Album.
Yellow Submarine did not reach number one in the United Kingdom or the United States, peaking at number 3 and number 2 respectively. It did top the charts in Canada, where it held the RPM national albums chart for two weeks.
George Martin, the Beatles' producer, composed the orchestral film score that fills the second side of the album. His selections were re-recorded with a 41-piece orchestra over two sessions on the 22nd and the 23rd of October 1968 at Abbey Road.
The Beatles recorded four new songs for Yellow Submarine: George Harrison's "Only a Northern Song" and "It's All Too Much", Paul McCartney's "All Together Now", and John Lennon's "Hey Bulldog". The other two Beatles tracks on the album, "Yellow Submarine" and "All You Need Is Love", had been previously released as singles.
A five-track mono EP containing the four new Beatles songs plus "Across the Universe" was mastered in March 1969 but never released. The EP was abandoned partly because excluding George Martin's music would have denied him contractual royalties. The mono mixes from that EP were first released publicly in 2009 on the Mono Masters collection.