How to build a custom AI assistant for a product or website?

Building a custom AI assistant usually starts with defining a narrow set of tasks it should handle well, then connecting an LLM to the relevant data sources through retrieval or function calling so its answers are grounded in the product's actual content rather than general knowledge. From there, the harder work is usually the surrounding product, handling conversation state, fallback behavior, and integrating the assistant into the existing UI, rather than the model call itself.