Describe the problem in ordinary language
Name the person facing the problem, the situation in which it appears and how they handle it today. Keep the description separate from the product you hope to build. That makes it easier to notice an answer you had not expected.
Choose a small learning step
A conversation, a prototype or a manually delivered example may answer an important question before software is needed. Decide what you are trying to learn and record the assumptions behind the experiment.
Turn the learning into a brief
Write down what changed your understanding and what remains uncertain. Choose the next practical step, with an owner and a review point. This is a product-discovery exercise, not legal or financial advice about setting up a company.