Clarify means to clear up confusion and make it all understandable. In a heart-breaking text, she clarified that she never ever wanted to see him again. It also means to remove impurities in a liquid; you clarify butter by gently heating it.
Clarify and clear are related, of course, and clear means you can see right through it. If you clarify your intention or your meaning, others will understand it clearly. If you aren't clear at the outset, you might find the need to clarify what you want later.