Internalizing is when Actors develop a deep personal understanding of what the character is really like.
The Actor will ask the questions Who? What? and Why? to better internalize their character. Once the character has been internalized, the actor is able to respond in character to any given situation.
Externalization is the process by which the true personality of a character is made visible to the audienuce.
A actor most carefully interpret, nonverbal expression, voice quality, pitch, rate, and physical action. This also requires lots of practice, emotion, and being able to make the crowd feel everything how your character.