Annie's Song is was originally released in 1974 on John Denver's eighth album Back Home Again and is one of his most popular songs. The song features a fingerpicked acoustic guitar throughout the song. There are nine chords in total and they are used to great effect here with a nice descending bass line of notes from the D major scale in the verses (D, C#, B, A, G, F#, E). The song is in the key of G and is originally played at approximately 147bpm in 3/4 time, although the tempo of the song does vary slightly between verses.
A quick note about the accidentals, passing notes or "wrong notes" when changing between chords. The reason they are used is that in some cases on guitar, as the fretting hand changes between chords, the picking pattern of the song is maintained by playing one open string before the next chord is formed. These are intentionally written in the guitar tab, and care has been taken to make sure that they are as accurate as possible to what is played by John in the original song.