Since the playwright cannot provide any description beyond a few notes to the actor/producer, character must be created through action and dialogue -- by what a character does and says.
In drama, action does speak louder than words and offers a reliable guide to a character's nature.
Nevertheless, what characters say about themselves or one another is the chief means of character development. Of course, what a character says about himself or others may not be true since the character may be lying or incapable of seeing the truth. What characters say about another character, though, deserves close attention, although it, too, may be false. Having minor characters talk about a main character before his arrival often guides our response once we meet him.
Costume, physical appearance, movement, gesture and speech habits are also used to convey character.
The constraints of performance time prevent the development of many complex or well-rounded characters. Character portrayal is often achieved by using stereotypical or "stock" characters whose traits are easily identified.
Trying to explain how you would portray a character in a particular scene and why often provokes a deeper understanding of a character's nature and motivation.