Stud in the context of people usually means an attractive, fit guy. So a very sexy man would be called a stud. "stallion" is a type of horse and can be used in the same way. In this context, it means an attractive man, which derives from the more literal term of a male bull or horse used for breeding.

What does it mean to look like a stud?

That means "You are very handsome/attractive"

What does it mean when a guy is a stud?

countable ​informala man who is admired for being sexually attractive and good at sex. He thinks he's such a stud. Synonyms and related words. Sexually attractive men.