Short answers, pulled from the story.
K-On! is a four-panel manga series written and illustrated by Kakifly, following four high school girls who join their school's light music club to prevent it from being shut down. It was serialized in Houbunsha's Manga Time Kirara magazine from May 2007 to October 2010.
The anime was produced by Kyoto Animation, directed by Naoko Yamada, and written by Reiko Yoshida. The 13-episode first season aired on TBS in Japan between April 3 and the 26th of June 2009, followed by a 26-episode second season between April 7 and the 28th of September 2010.
The second season's opening theme, "Go! Go! Maniac," became the first anime image song to reach number one on the Oricon singles chart. The voice cast also became the first female vocalists to hold the top two chart positions simultaneously in 26 years, a record previously set by Seiko Matsuda in 1983.
The K-On! film, released on the 3rd of December 2011, opened at number two with a gross of just over 317 million yen from 137 theaters. Over its full run, the film earned just under 1.64 billion yen in Japan.
The rural town of Toyosato in Japan became a tourism destination because its elementary school served as the architectural model for the high school in the anime. The school opened portions of the building as a public exhibit dedicated to the series.
Yui Hirasawa plays a Heritage Cherry Sunburst Gibson Les Paul Standard electric guitar, Mio Akiyama plays a left-handed 3-Color Sunburst Fender Jazz Bass, Ritsu Tainaka plays a yellow Rick Marotta Signature Yamaha Hipgig drum kit, Tsumugi Kotobuki plays a Korg Triton Extreme 76-key keyboard, and Azusa Nakano plays a Fender Mustang electric guitar she names Muttan.