The event is open to anyone and free to attend, as long as you register now while there’s still space: https://android-developers.googleblog.com/2017/08/announcing-20-finalists-and-open.html
Out of the 20 games selected to exhibit, 10 will be chosen by audience voting to present on stage, and then 3 winners will be chosen by a panel of judges.
In Google’s words: To celebrate some of the latest innovative indie games on Google Play, we’re hosting the second Indie Games Festival in North America on September 23rd in San Francisco. At the festival, Android fans and gamers will have a unique opportunity to play new and/or unreleased indie games from some of the most innovative developers in the US and Canada, as well as vote for their favorite ones.
It’s great to have an opportunity to work with Google to bring digital-first board games to more players. We are thrilled to be a part of this event, and we hope to be able to meet some of our fans there as well!