"清晰明白地说" can be translated into English as "speak clearly and understandably" or "express oneself clearly and explicitly".
"Speak clearly and understandably" emphasizes the clarity and ease of comprehension in verbal communication.
"Express oneself clearly and explicitly" is more general and can apply to both verbal and written expression, highlighting the importance of being precise and unambiguous.
Choose the phrase that best fits the context of your sentence.