Surprisingly, we didn't really teach him most words and it was through context like yours. Teaching him mostly seems to backfire (i.e. "You want me to say that? Well I'm going to refuse to do it!"). The only one we might have taught him was "peek-a-boo", but even that has context, since he'll say it when we cover his head or we try to hide from him. Sometimes he'll hide behind my laptop, poke his head out and say it when he's trying to get my attention.

I guess I did teach him to say "yeah!". It became his alternative to express any excitable emotion instead of screaming. Usually comes with a little head bob at the same time for additional cuteness. He heard the song "Mi Gente" in a commercial once and when they say "yeah yeah yeah", out of nowhere he I hear him respond back with a "yeah!".

The first thing he learned was his name, "Willy", and for the longest time I thought he would just be a Pokemon...forever saying his name with different intonations depending on what he was trying to imply. I think he picked that up within his first year or so. Then he learned a few more. After 6 years he might be up to 12-16 now. Could be more, but he says a lot of gibberish that hasn't formed into words quite yet.

Perhaps my favorite is when he says he's a "good boy" and he just did something bad. Little jerk knows exactly what he's saying, but we love him anyways.

I can't really get him to do tricks yet, other than spinning in a circle. He's highly treat motivated, so anything that results in getting food will usually work if you keep at it. I'm trying to get him to try on a flight harness so we can take him out and about with us more often. He likes people, but he could be more socialized.

Guessing you have a green cheek as well? We have a cinnamon variation. I think they're a bit odd, but that could be GCCs in general as we've only had 1 and a budgie.