How do AI search features find and use business websites?
Mostly the same way search engines do: pages must be crawlable, indexable and genuinely useful. There is no special markup or score that guarantees inclusion.
Google states that the same SEO fundamentals apply to its AI features (AI Overviews and AI Mode): a page must be indexed and eligible to appear with a snippet in Google Search to be shown as a supporting link. Google says there are no additional requirements or special optimizations needed.
ChatGPT search uses a crawler called OAI-SearchBot. OpenAI documents that sites which allow OAI-SearchBot in robots.txt can appear in ChatGPT search results; blocking it can keep a site out of those answers. That is separate from GPTBot, which OpenAI uses for model training.
In practice, the most useful thing a small business can do is answer the questions customers really ask, clearly and accurately, on pages that crawlers can reach. Treat any tool that promises a guaranteed 'AI ranking' or a proprietary 'AI visibility score' as unverified.