Two things, and one decision.
A connected Google Ads account - the wizard lists the accounts linked to your agency; you pick which one the campaign will be created in.
A landing page URL - the only input the AI needs to understand your business.
Use the page that best represents what you want this campaign to sell. If the campaign is for the whole business, a strong homepage works. If it's for one product line or service, use that page - the AI builds its entire understanding from what it reads there, so a focused page produces a focused campaign.
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The Setup step
Name, goal, voice, account and URL - the five inputs.
Discovery - how the AI learns your business
Your page is read and distilled into an expert brief.
Best practices
The habits that separate good campaigns from great ones.