It is a AI-powered SQL generator. You tell AI what SQL you want using everyday language and will generate an optimized (if possible) SQL query with database indexes. If you don't need database indexes, using the "default" SQL generator is recommended.
It depends on what you want to achieve, but instructions like "Get customers from this month" or "Get customers within 500m of the Eiffel Tower using lat/lng" are some examples. You can see SQL examples here. It shows what you can ask AI and what it generates.
Adding your custom data source improves the accuracy. AI is then often able to infer table and column names like foreign keys.