Comely means attractive or appropriate. A comely girl is pretty. A comely hairstyle makes you seem prettier maybe than you are. If your manners are comely, it means you know the right way to act to put people at their ease.
Comely is related to the word becoming, in the sense of something's being attractive and appropriate––you're comely wearing that becoming blouse, the way she told the story was becoming to a comely young lady. Comely is the opposite of the similar-looking homely, which means plain-looking, almost ugly.