To make something clearer or easier to understand by giving more details.
“I am writing to clarify a few points regarding the invoice you sent last week.”
“Could you please clarify which documents are needed to process the refund?”
Pay attention to who is doing the clarifying: 'I am writing to clarify' means the writer is explaining something, while 'could you clarify' means the writer is asking a question. Mixing these up is a common trap in Reading Part 1 purpose questions.
Synonyms: explain, elaborate, spell out