'Advanced' is a general term used to indicate less common usually altered chords and progressions.
Actually chords are very simple, not vast, because there are only 3 common chords, - major, minor and diminished. Everything else is an altered or extended version of these and the alterations are generally obvious from the chord name. Eg 9th means add a 9th, 6th means add a 6th, b9 means add a flattened 9th. Sometimes there is more than one alteration. The numbers are just the note of the scale in that key. One slight complication is that there are two common versions of a 7th you have to learn to recognize.
The theory is simple, the difficult part is learning to play them seamlessly, without thinking. This is where the real work is because if you can't play a G, Em, Am, D progression rapidly and easily, almost without thinking, there is little point worrying about whether it should be G6, or Gb9, or G/A!
Dont overthink the theory, just learn to play the basics. Move on when it is mastered.
BTW - in many cases the extended chord designation is just a formal recognition of a note that is simultaneously happening in the melody, and doesn't have to be included in the chord because you are playing it anyway the melody.
Mike