When you're attired, you're dressed in clothing. The bride in a wedding is traditionally attired in an elaborate white gown.
While you can use the adjective attired to describe anyone who's wearing clothes or accessories, it's most often used to talk about formal or elaborate clothing. Everyone at your masquerade ball might be attired in fancy costumes, and you could describe the flashily attired attendees at a high school prom. The root of attired is the Old French atirier, "to equip or prepare."