The melody of 21 Guns by Green Day runs 359 notes across 59 bars, 5:00 long in Bb at 84 beats per minute. The tab sits almost entirely in the first two frets, one note at a time — no chords to barre and no strumming pattern to keep up with. A piano backing track plays the chords and bass underneath, so the line you are learning sounds like the record even at half speed.
Prefer to strum and sing it instead? 21 Guns chords and lyrics.