As the others have said, we usually use "crystal clear" to mean "extremely easy to understand." Normally we don't say that a person is crystal clear. We use "crystal clear" to describe things like instructions, directions, descriptions, orders, or writing (especially essays that are intended to give information or prove something). If someone says that a person is crystal clear, it probably means that what the person says is always very easy to understand.

Hi Baboon ☺️ it means being extremely clear or easy to understand.

An explanation is cristal clear when it is very clear (clear like a cristal). Someone is being cristal clear when he or she is explaining something very clearly... I would say.