Yes. Especially the main characters and any characters that have an accent or dialect and what that is. This is very valuable to the narrator to convey the characters most accurately to your vision. It will help you get the end result you are hoping for. You can describe your characters in whatever way is easiest for you. For example, you could say a character reminds you of Mr. Darcy in Pride and Prejudice, when played by Matthew Macfadyen; or that this character has a mousy voice. Anything helps. You do not need to list every walk-on character who appears briefly, although if you have strong ideas about any characters, it’s helpful to let your narrator know at the beginning.