I was able to opt-in for search ads, but I don't find anywhere the screen where I can create these ads?
How can I create a search ads campaign?
Search Ads haven't been fully released yet. They're going to be run in beta during the summer, during which opted-in apps will be run as ads for free while they get the format figured out. Expect more information later today at WWDC.
Apple confirmed they're 100% free, not priced or subsidized? That would be pretty nice of them but would also require a potentially stringent approval process vs just "opting-in."
I also imagine Apple wants to start calibrating its pricing auction sooner than later.
They are running them for free because they will be auto generating them for you. You do not get any say in keywords, etc, they will publish the ads:
"Participation is free. There is no setup, budget or bidding required by you. Test ads will be automatically created with the information you already provide to the App Store. While data for how your app performs will not be available, and there’s no guarantee an ad for a specific app will be shown, you may generate downloads as a result of your participation."
The same to you.
Did you create it?And how to do?
I'm a US developer. How to create a campaign?