By definition, a chord is just 2 or more notes being played together. But don’t worry we not need all such chords to become professional guitarist. You can start learning following chords in order.

However, if you’re talking about just normal chords – here are the chords that do not require a Barr to be played.

A, Am, C, D, Dm, E, Em, G

Many other chords can be played with modifing the Barr (so you don’t actually need to play the chord with your while index finger laying across a fret).

These chords are:

F, B, C#m, F#m, G#m

If you learn all these chords, you’ll be in great shape as a guitarist. Keep in mind, none of these are “7” chords. You can almost immediately increase the amount of chords you know just by adding the 7th to a given chord. I would learn these 7th chords:

A7, CM7, D7, DM7, Dm7, E7, Em7, FM7, G7

The “M7” means major 7th. The “m7” means minor 7th. The 7 immediately following a note name means a “Major-minor 7th” – or, for simplicity sake – a “7th”.