Transposing means moving music to another key: every note goes up or down by the same number of . The melody stays the same tune; it just starts on a different note. Singers do it to fit their voice, guitarists to use easier chords.
Here's the start of Beethoven's "Ode to Joy" in C major:
Written as it's 3 3 4 5 5 4 3 2 1 1 2 3 3 2 2, and that's true in every . To transpose it, take the same degrees from another key's scale. Pick a key's root note:
In G major every note is 7 half steps higher than in C. The shape of the melody on the staff stays the same; only its place and the key signature change.
Musicians often write as numbers instead of names: I is the chord on the key's 1st note, V on its 5th (more in the Chords chapter). Capitals are major chords, small letters minor ones, and a chord name like Am means A minor. Those numbers don't change when you transpose: I–V–vi–IV is C G Am F in C, and G D Em C in G.
A capo is a clamp you put across the guitar's neck. It raises every string by one half step per fret, so the chords guitarists learn first (you'll meet them in Chords on the Guitar) sound higher. A chord's shape is how your fingers hold it: with the capo on the 3rd fret, fingering a G chord sounds B♭, the C shape sounds E♭, and so on.
That lets you play in any key with the easy of C, G, D, A or E. Some shapes include a (the F in C, the Bm in D), which is why G shapes are often the easiest choice. Pick the key of a song to see where to put the capo:
I–V–vi–IV in B♭: put the capo on fret 3 and play G D Em C. It sounds as B♭ F Gm E♭.
The diagrams show the shapes as you finger them, counting frets from the capo as if it were the nut, the strip at the top of the neck where the open strings stop. Lower capo positions sound fuller; higher ones brighter.
Next: Chords