Our Self is made up of many levels. The koshas are considered the layers of the Self. Manomaya is the layer within which the mind or manas and the emotions are prominent.
Our mind is constantly chattering away. It tells us our desires, needs, dislikes, etc. All of these things are directed by the ego. The ego places labels upon everything we experience. Our emotions are attached to these experiences and, through them, we develop samskaras or impressions.
Manomaya is the layer within that we must work the hardest to move beyond. If we can let go of our ego then our mind can quiet. If we can move beyond our emotions, we can view the world with less bias and judgement. Our practice is to let go of these things and become less attached to our self and that which lies outside of us.