Hi Joaquin!

The regular names, G, and Gm, you would use when you only have the three notes of the basic major or minor triad in the chord. These notes are the root (1), the third (major or minor), and the fifth.

G (G major): G (1), B (major 3rd), D (fifth)
Gm (G minor): G (1), Bb (minor 3rd), D (fifth)

Sus2
Gsus2 has the 2 (or 9, same note) in the chord, but the 3rd is missing. The 2 (or 9) is the 2nd note in the scale, in this case A, because it's the second note of the G major scale.

Sus4
Gsus4 contains the 4th in the chord, instead of the 3rd. This note is C (instead of the 3rd B).

Gadd9
In a Gadd9 chord, you have the 9 (or 2, same note) in the chord, and you also have the 3rd. This is the difference between the sus2 chord and the add9 chord.

G9
Here you have the 9 again, as well as the 3rd, but also the b7 (flat seven). So we have G, B, D, F, and A. The 5th (D) is sometimes skipped.

G11
Here we have the 11th note from the scale in the chord, but also the b7, and sometimes the 9. The 11th note is the same as the 4th, which is C here in the key of G. But you call it a G11 chord if you also have the b7 note (F) present.

Dom
The term dominant (dom) usually refers to the kind of 7 a chord has. If it has a b7 (and a major 3rd) it is called a Dominant 7th chord. If it has a regular (major) 7 (and a major 3rd), it is called a major 7th chord.

So, in the case of G - G7, is the same as G dominant 7. And Gmaj7, is pronounced G major 7. A G9 (G dominant 9) has the b7, and a Gmaj9 has the regular major 7 in it. Plus of course the 9th.

Dim means diminished (which basically means lowered). This usually refers to the 5th or the 7th.

A diminished triad contains the root (1), minor 3rd, and a diminished 5th. This means that the 5th is lowered one half-step compared to a regular minor triad.

Notes in a G diminished triad: G (1), Bb (minor 3rd), Db (diminished 5th).

A half-diminished seventh chord has the root (1), minor 3rd, diminished 5th, and b7.

A diminished seventh chord has the root (1), minor 3rd, diminished 5th and a diminished 7th, which is a half-step below the b7, sometimes written bb7.

This is complicated stuff, so take your time with this and eventually it will seem natural!