True Self is your conscience without your Ego.
As a human, you have a mind that receives logic from your brain and feelings from your soul. The mind filters both types of information and the end result is your conscience.
As a child, the mind typically allows feelings to take the dominant role in your conscious mind and is therefore mostly lead by your soul. As you go through various experiences in life, your Ego starts developing your character. Think of your character as a role that you play in order to protect your soul from getting hurt by others or to fit into society.
For example, little Jim runs over to a group of kids and wants to be friends. The kids laugh at him and make fun of his favorite jacket because it has a puppy design on it. As he’s being ridiculed, through angry tears, Jim’s Ego steps in to protect his soul from getting hurt further by deciding that puppy designs are stupid. Going forward, Jim would think that he’s against this design regardless of how he truly feels about it. In fact, there is a good chance that Jim will make fun of other children who wear a similar design. Jim would now define himself more by his character than by his True Self.
True Self is the part of you that’s hidden within your character. It is the feeling and sometimes even the voice we hear when we are in need of guidance. It is who we are without the protective layer of Ego.
The combination of True Self and character is what defines a person.