There are a number of excellent articles over on the website of the American Association of Community Theatre.
This is the third in a series of extracts from those articles and a link so that if you want to read more you can get to the entire article.
The third one is about the role of The Costume Designer.
Costume designers create the look of each character by designing clothes and accessories the actors will wear in performance.
Depending on their style and complexity, costumes may be made, bought, revamped out of existing stock or rented. Their designs need to faithfully reflect the personalities of the characters in the script.
The shapes, colors and textures that a costume designer chooses make an immediate and powerful visual statement to the audience. Creative collaboration among the costume designer, the director and the set and lighting designers ensures that the costumes are smoothly integrated into the production as a whole.
Stage costumes can provide audiences with information about a character's occupation, social status, gender, age, sense of style and tendencies towards conformity or individualism. As well, costumes can:
reinforce the mood and style of the production
distinguish between major and minor characters
suggest relationships between characters
change an actor's appearance
suggest changes in character development and age
be objects of beauty in their own right.
Costume designs also need to include any accessories such as canes, hats, gloves, shoes, jewelry or masks. These costume props add a great deal of visual interest to the overall costume design. They are often the items that truly distinguish one character from another.
The complete article can be found here.