Noticing a dark patch is the first step, and every later step depends on how well you describe what you saw. This guide takes the process in order. It stops before treatment, which has its own reading, such as this PubMed Central review of cosmeceuticals for hyperpigmentation.
Step one: put the right name on the spot
Cleveland Clinic notes that other names for liver spots include age spots, sun spots and solar lentigines. Keep all four terms in mind as you read, because they point at the same kind of spot.
What to gather before anyone examines it
Collect what you can describe. Note where the spot sits, when you first noticed it, and whether it has looked the same since. Take a clear photo in daylight and date it. Add a list of the skin products you use now. Reading a plain overview such as Cleveland Clinic's page on liver spots while you do this is a reasonable way to prepare your questions.
Where age fits into the picture
Cleveland Clinic also states that liver spots are more common in adults over 50. Treat that as context, not a ruling. At any age the spot still gets the same description, the same photo and the same date.
Walking the spot through three checks, in order
First, look at it in daylight and write down its color and edges in your own words. Second, photograph it beside a coin for scale. Third, repeat the photo on a set date later, so you hold a comparison instead of a memory. For general background on how skin changes from the sun are discussed, Cleveland Clinic's overview of sun-damaged skin is a useful companion.
When an examiner's view of your spot differs from written guidance
Written resources describe a condition in general terms. A practitioner who examines your skin speaks to your case. When the two differ, do not simply pick the one you prefer. Ask what in your history or your skin explains the difference, and write the answer next to your photos.
Taking your spot file to a professional look
With a name, a photo, a date and a short note, you are ready for a professional look. Take that file with you. From there the conversation moves to options, and the American Society for Dermatologic Surgery's sun damage page is worth reading beforehand.