In 3 easy steps-

1. Learn how to play the following chords: G major, D major, C major and A minor (4 of the simplest chords in the known universe).
2. Find the tab for Bob Dylan’s “Knockin’ on Heaven’s Door”.
3. Practise till your fingers bleed (figuratively) until you get it just right (use your own judgement by ear).

Congratulations! You’re a guitarist.