What do I do after catching the Unowns in Pokemon?

Nothing, you just have them. there isn’t anything except being able to say that you got them.

well what else is there to do in the game now? i beat both region gyms, beat Red, I believe I have all the legendary pokemon…do I just build up my pokedex?

I don’t know, all I did was google search. Maybe just replay the game.

I think there is a dance you’re supposed to do? I forget…

You can still do Battle Frontier, I believe. Earn BP there to purchase useful battle items, TMs, et cetera.

You said you have all the legendaries? Make sure to get Mewtwo in the Cerulean cave and (if you have SoulSilver) Groudon in the Embedded Tower. You’ll need to have gotten a Kanto starter from Oak for this.

And although it isn’t legendary, you can obtain a Lapras every Friday in Union Cave.

You can also go here for guides, if you’re interested.