In particular guitar players are a little puzzled by the whole 4-part thing as so many chords they play have 5 or 6 notes. So what gives? The answer is that octaves of a chord tone are not considered. Taking the E chord as an example. It is the one guitar chord that everyone knows and it is played on all six strings. Behind the misnomer lurks an E major triad, a chord that harmonically speaking only has 3 notes: three Es, two Bs and a G#. We could also say, the E major triad contains a root (E), a major 3rd (G#) and a perfect fifth (B).
But why toss out the octaves? There are several reasons for that. First we need to consider the purpose of harmony in general. Harmony is an attempt to categorize and classify what happens when notes are sounded together. With it we can harmonize melodies, transpose songs and communicate to each other what we are doing. But it is complicated. To be able to reduce the available spectrum of notes to 12, which follows logically once we toss our octaves, makes our lives that much easier. And we can do this because of one important fact, any note already contains its octave as an overtone. Depending on the instrument it is more or less audible, but it is there.
So if a song calls for an E maj triad at a specific place, it doesn't matter how many Es I play, as long as there is at least one. I am also required to play at least one B and one G#. This is the way we are trying to look at harmony with ChordLab. Not with a memorized pattern, but with music notation, chord tones described in their function, and chords generally classified by their inversions and voicings.