How to read guitar chord diagrams
A chord diagram is a photograph of the neck, taken from the front, with the guitar standing upright. Everything follows from that.
A chord diagram is a photograph of the guitar neck, taken from the front, with the instrument standing upright. Everything else follows from that.
This is step one of the guitar path. If you want the reasoning underneath the diagrams, the music theory path covers where chords come from.
Orientation is the whole trick
The six vertical lines are the strings. The leftmost is your lowest string, the thickest one. The rightmost is your highest, the thinnest.
This confuses almost everybody at first, because when you look down at your own guitar the low string is nearest you and appears on top. The diagram shows the neck as if it were facing you, standing up. Get that picture in your head and the rest is straightforward.
The horizontal lines are frets. The thick line at the very top is the nut — the end of the neck. If a diagram starts somewhere further up, a small number beside it tells you which fret.
Dots, circles and crosses
A dot means press that string at that fret. A number inside or below the dot tells you which finger: 1 is the index, 4 is the little finger.
An O above a string means play it open, without pressing anything. An X means do not play that string at all — mute it or skip it.
Those five symbols cover essentially every chord diagram you will ever encounter.
Why the shapes look random and are not
Chord shapes seem arbitrary when learned one at a time. They are not. Every shape is the same handful of notes arranged in whatever order the tuning makes reachable.
The reason an open G looks nothing like an open D is that standard tuning is not evenly spaced — there is a deliberate irregularity between the third and second strings. That single quirk is why guitar chord shapes look inconsistent while the underlying theory is perfectly regular.
Learn the shapes first if you like. But at some point, learn why they are shaped that way, because that is when the neck stops being a memory test.