解惑 is a formal verb meaning 'to dispel doubts' or 'to clarify confusion'. It's a separable verb (离合词): 解 ('resolve') and 惑 ('doubt') can split when you insert a measure word or object, e.g. 解了惑 ('resolved the doubt'). You often see it in the four-character phrase 答疑解惑 ('answer questions and resolve doubts'), common in academic or advisory contexts.