When pitches are combined together, chords are made.
Triads include three diffent pitches. The most common chords are major triads, minor triads, augmented triads, diminished triads. Suspended second and suspended fourth also consist of three different notes, but because of the different intervals between notes and notes, we don’t name them with “triads”.
Seventh chords consist of four different notes. Dominant seventh, major seventh, minor seventh, diminished seventh, half-dimished seventh, augmented seventh, augmented-major seventh, minor-major seventh will be introduced here.
Of course there are ninth chords which consist of five notes or even eleventh chords, thirteenth chords, etc. Although sometimes people use them in popular songs, I will not do further introduction here.
The figure below shows these chords with root C.