Start with the requested action
Locate the notice number, affected year, explanation, and response instructions before naming the problem in your own words. Keep the full letter available while making notes. A proposed change, an information request, and a stated balance may lead to different questions, so a familiar layout should not determine the response.
Match the explanation to a source
Place the return or statement for the period beside the line you want to understand. If a payment is relevant, keep its confirmation with the intended account and date. Record what the letter says, what your evidence shows, and what remains unclear. That comparison is more useful than assuming the amount is either automatically right or automatically wrong.
Preserve the action trail
Follow the instruction applicable to the actual notice and retain a copy of any response and its delivery evidence. A conversation about help does not replace the required account action. If professional work is proposed, ask who reviews the question, what records are needed, and who handles submission. Add later correspondence to the same file so the first letter remains connected to what followed.