The most commonly used chords are constructed from stacked thirds. Chords can also be constructed from seconds, fourths or fifths but these types of chords are less common.
However, if you happen to stack another third onto any of the basic chords you will now have a Seventh Chord.
The names of the chords from left to right are:
Anything past a seventh chord is considered and extend chord. If you happen to stack a third upon any seventh chord you will get a ninth chord. If you then stack another third upon your ninth chord you will get a eleventh chord. And finally, if you stack on more third upon an eleventh chord you will get a thirteenth chord.