For general questions about chords like how to play them, construct them, or what symbols represent them. For more in depth analysis of the ideas behind chords themselves, please use the chord-theory tag.
See also harmony, which is more general and covers notes being sounded together with different relationships, and the way those relationships change over the course of a piece.
Chords in a Western context are typically constructed in thirds and because of this the name a chord largely depend on the interval between the root note and all the other notes of the chord. The basic naming scheme also reflects this.
There are other methods of building chords for example quartal where chords are built in fourths and quintal where chords are built in fifths.