is it a real audience?

In most episodes there was a live audience. However, episodes that contained important storylines یا surprises, یا scenes shot outside of the usual set (any of the apartments, Central Perk etc,) would usually be filmed without an audience either because of space یا because the producers did not want anything leaked before an episode aired. In these cases they would use a laughter track. The most significant of these was the final episode ever.
I should say, though, that some episodes filmed entirely without the usaul set did have a live audience, because the setting was so important for the storyline - they would then most likely film in another studio (i.e. TOI Vegas).
Hope this makes sense. :D

in most episodes, yes! but in some episodes the producers prefer NOT 2 have a "laugh" moment because the actions r pretty important یا there isn't any space! and sometimes, as i watched on the special features of my complete seasons box, the laughter sometimes is 2 hard, ur not able to hear the actors, so they use another laugh track recorded earlier!!! hope i helped! :)

no I dont belive it is a real audience but it always makes me laugh

most are live! some though they had to do without an audience so its autotuned

Its a real audience.
They perform for them, and if everything needs editing they do they before its launched.

yes

Yes is it