Jungian terms defined
I find it hard to talk about Sandplay without using some of the Jungian terminology. Therefore I thought it would be helpful to put short definitions for a few of the terms used.
Consciousness is that of which we can be aware. "Coming to consciousness" is developing ego strengths or what we today would
call executive functions.
Personal Unconscious is created by repression. If we find something unacceptable or intolerable we repress it into the Personal Unconscious.
Archetypes
A formless pattern that underlies both instinctual behaviors and primordial images. For example, at the core of a mother complex is a mother archetype. They tend to be less personal (my mom) and more rooted in the experience of the cultural heritage (the Great Mother) whether or not the person has any personal knowledge of the image or behaviors. They are the seeds of psychic experience and the inherited component of the psyche. Joseph Campbell’s study of the archetypes was made popular through his book The Hero with a Thousand Faces (1949) and the PBS series featuring interviews with him.
The Collective Unconscious is made up of instincts and archetypes. It is thought to contain the whole spiritual heritage of humankind's evolution.
The Self is the Archetype of wholeness and transcendence, sometimes represented as the Wise Old Man or Wise Old Woman (but which takes a wide variety of human, animal and abstract forms.) It is the directing center or the central organizing principle. It is the guiding center of development and the goal of life itself.

The Ego discriminates among the contents of the psyche. It's job is to control instincts and help us adapt to cultural norms. I tend to think of a car as a metaphor for the Self and the Ego as the metaphor for the driver. We talk about ego strengths such as self-observing, reflecting, and emotion regulation. In Sandplay we see these concretely worked on in the sand. The ego is what helps us get through the day.
The Personal Shadow consists of the features of the personality that we strive to hide or have never known. The Personal Shadow serves as a connection to the collective unconscious.
The Personal Shadow consists of the features of the personality that we strive to hide or have never known. The Personal Shadow serves as a connection to the collective unconscious.
Union of Opposites

We all have two sides. The Asian cultures refer to it as the Yin and the Yang. In our culture we talk about masculine and feminine. As we work toward Individuation we obtain the union of our two sides, known as the union of opposites.