Microphone is a voice agent. You talk; it writes the brief you would otherwise stall on typing. That brief is the input to everything downstream, which is why the quality of the conversation determines the quality of the test.
What to say
Hold the microphone and describe the idea the way you would describe it to a friend who asked a sharp question. Say who has the problem, specifically enough that you could name three real people. Say what they do instead right now, including the ugly workaround. Say why that fails and what the failure costs them. Say what you would charge.
Apple Notes can sit next to the conversation if that is how you already think. The recording should be the primary source, not a supplement to a document you wrote first.
What comes back
A problem statement — one sentence you would be willing to spend money against. Hypotheses that each name an audience and a claim you can put in an ad. Market research drawn from the same conversation: who else sells a fix, how they describe it, and where the people with this problem already gather.
The detailed version is in the guide on writing a problem statement from a conversation.
What comes next
The conversation is the source for ads and campaigns. Social work comes later, as social media subagents — a handoff, not a second product. The reasoning behind that split is in one voice agent.