Basics
How a chord is built
A chord is notes stacked in thirds; the arpeggio is those same notes played one at a time.
Take a scale and stack every other note: start on the root, skip one to reach the third, skip one more to reach the fifth. Root–third–fifth is a triad — the smallest chord.
The gaps are measured in tones (T, 2 frets) and semitones (½, 1 fret) — the same ruler as the scales. A major triad is the root, a major third (2 tones / 4 frets) and a perfect fifth (3½ tones / 7 frets). A minor triad flattens that third to a tone and a half (3 frets). The third is what makes a chord sound bright or dark.
Stack one more third and you get a four-note seventh chord. Gypsy jazz lives on these four-note colours — 6, m6, 7, maj7 — rather than bare triads.
An arpeggio is the exact same notes, played one after another instead of together. Learn the chord and you already know the arpeggio: that's why chord shapes and solo lines connect on the neck.