Why is my PyGame Sprite, in a Group, not drawn - AttributeError: 'Group' object has no attribute 'blitme'

The method blitme doesn't exist in pygame.sprite.Group. You cannot invoke a method on a pygame.sprite.Group object, that doesn't exist. But you don't need blitme at all. All you have to do is to invoke pygame.sprite.Group.draw():

Draws the contained Sprites to the Surface argument. This uses the Sprite.image attribute for the source surface, and Sprite.rect for the position.

For instance:

letters.draw()

pygame.sprite.Group.draw() and pygame.sprite.Group.update() are methods which are provided by pygame.sprite.Group.

The former delegates the to the update mehtod of the contained pygame.sprite.Sprites - you have to implement the method. See pygame.sprite.Group.update():

Calls the update() method on all Sprites in the Group [...]

The later uses the image and rect attributes of the contained pygame.sprite.Sprites to draw the objects - you have to ensure that the pygame.sprite.Sprites have the required attributes. See pygame.sprite.Group.draw():

Draws the contained Sprites to the Surface argument. This uses the Sprite.image attribute for the source surface, and Sprite.rect. [...]