Unlike humans, parrots do not own vocal cords. Instead, they learn to control the movement of the muscles in the throat to direct the airflow within such a way as to reproduce certain tones and sounds—sometimes even human sounds. Parrots associate when to say a positive word and what to say like when you come into the room your parrot might read aloud "hello" But there are still other parrots who just verbalize randomly. They aren't the only bird who can talk, mynah birds can too.
I know it has a lot to do near their throats/tongues. For example, toucans have a tongue that looks like a thin barb and it's impossible for them to make the pronounciation we do with their tongues. Parrots are able to do it though beside how theirs are.
A copycat can't really speak so much, they imitate what they hear, they don't have the understanding of spoken communication that humans do.
As for other birds, yes, a few other birds can mimic human speech, like the mynah bird