Answer by taking a quote from the following article:

"Man on the Moon" is a song by the American alternative rock band R.E.M., released as the second single from their 1992 album Automatic for the People. The lyrics were written by lead singer Michael Stipe, and the music by drummer Bill Berry and guitarist Peter Buck, and credited to the whole band as usual. The song was well received by critics and peaked at number 30 on the Billboard Hot 100 and number 18 on the UK Singles Chart. It remains one of R.E.M.'s most popular songs and was included on the compilations In Time:

"Man on the Moon" is a mid-tempo country-rock song following a verse-chorus structure with an added pre-chorus and an instrumental bridge following the second and third choruses. The song is somewhat unusual in that the verses are unequal in length, with six lines in the first verse but only four in the second and third verses.  An early instrumental demo of the song was known to the band as "C to D Slide". Guitarist Peter Buck has explained how the music came together: "'Man on the Moon' was something that Bill [Berry] had, this one chord change that he came in with, which was C to D like the verse of the song, and he said: 'I don't know what to do with that.' I used to finish some of Bill's things... he would come up with the riffs, but I would be the finish guy for that. I sat down and came up with the chorus, the bridges, and so forth. I remember we showed it to Mike and Michael when they came in later; definitely we had the song finished. I think Bill played bass and I played guitar; we kept going around with it. I think we might have played some mandolin on it in the rehearsal studio."  Michael Stipe later explained in an interview with Charlie Rose how the lyrics were written independently of the music, which had no prior association with the song's eventual lyrical content regarding Kaufman. Stipe recounted that the rest of the members of R.E.M. had written and performed the music of the song and recorded it along with the rest of the Automatic for the People album during studio sessions in Seattle. As of the final week of the recording sessions, Stipe was still struggling to write lyrics for the song, and the other band members continued to plead with him to finish it. Stipe attempted to argue that the track should be an instrumental, but his bandmates were insistent. Stipe listened to the track on a walk around Seattle on his Walkman cassette player and was inspired to write about the performances of entertainer Andy Kaufman. After Stipe went back to the studio to complete the vocal track, the master was mixed that night and sent out the following day to be mastered.

what are the major instruments in the composition?
think Bill played bass and I played guitar; we kept going around with it.