Question: Where do you download games?

There is this game erthenal gates and I don't know where the download button is.

You can't download any games on this website, nor are people allowed to post links to other sites where you can download games. The most you can do is download a patch needed to make the game work, and that should usually be in the first post of the thread for the particular game, assuming it's developed far along enough for that. If your problem is with finding the download button on a different site, you'd probably want to contact whoever runs that site for assistance or something.

Is it not in the thread here?

https://www.pokecommunity.com/showthread.php?t=347265