Break On Through (To the Other Side) is one of The Doors staples tunes from their debut self titled album in 1966. Robby Krieger mostly used his fingers to play the guitar instead of a pick. Because of this, he incorporated string skipping into his playing more than most other players at the time. The riffs are fairly simple to play since they're based around pentatonic patterns, power chords, and open chords, none of which are very difficult. Robby would play power chords on the upper strings and then play the bass notes with his thumb to cover the entire sound spectrum which would normally be very difficult to do with a pick but is easy with your fingers.