The adverb evidently is used to describe something that's obvious or easily understood. The kids next door didn't even apologize for breaking our window with their baseball; they evidently have terrible manners.
When something is evident, it's plainly clear. You can use evidently when something couldn't be more obvious, whether you're describing a driver who evidently doesn't understand that a yellow light means "slow down" and not "speed up," or a typo-riddled book that was evidently published hastily. The evidence points toward these conclusions, in other words. The Latin root is evidentem, "perceptible, clear, obvious, or apparent."