Where am I able to find my gameid?

When you publish your game, you'll be given a URL. The game ID is the trailing part of that URL. For example with, the ID is 9b49b4/mergelandia. (There's also a longer form ID, in this case 9b49b4f42a754f48a57c41c0c8afd092. Both forms should work with things like the TransferToGame Lua function.)

You can find a list of the games you've already published by clicking your username in the top right corner of the website and selecting View Profile, then scroll down to My Games. You can do the same in the Core client, but to get the URL there's an extra step of clicking on the game, and then clicking a share button in the top right of the game details to get the URL.