There's no "right" way to start. Pick whichever matches what's in your head.
A website address
Point at a company or a specific product page (e.g. stripe.com or apple.com/apple-watch). Discover Agents reads that page and researches the space around it. A specific product page gives sharper results than a whole homepage.
An angle
An angle is a non-obvious lens to look through: a way of framing a search that turns up ideas you wouldn't list in five minutes. Tap one to explore the space through that frame instead of the obvious one.
A world
A world is a broad space (an industry, a field, a kind of customer). Because a whole world is often too broad to be useful, picking one reveals a row of sub-worlds: narrower slices inside it. Choose a sub-world to focus the research.
No company in mind? That's the point. Angles and worlds let you explore from curiosity, not just from a URL you already have.