Yoga sutra iii.7 “trayam antarangam purvebhyah”

“These three aspects of yoga are internal, compared to the former five.”
Within the eight limbs of ashtanga yoga there is a definitive change in focus in how we interact with the external word, outside ourselves, and our internal world.  The first five of the limbs build external focus. The yamas, niyamas, asana, pranayama and prathyahara help us to examine and understand our relationship with our mind, bodies and our interaction with and connection to the world around us.  We use these five aspects of yoga along with our bodies, minds and senses to understand how we are interacting with the world around us and how we should interact with the world around us.  We also use these aspects of yoga to guide us in our actions.
The other three aspects of yoga in the sutra, dharana, dhyana and samadhi are internal in nature.  They help us to understand our relationship to ourselves.  They are integral in our understanding the difference between our ego, mind and consciousness.  It is only when we are paying attention to our internal environment that we know which part of our  brain or self, is in control and how it is controlling us.  Is it the ego telling us we can do better or our consciousness knowing that we are living our truth.  When we are experiencing any of these three aspects of yoga we are not in relationship outside ourselves.  We are in fact inside ourselves and separate from external stimulus.  It is only during this time that we are our world and not in an egotistical way, but learning and knowing ourselves to lessen our egotistical ways.

Yoga sutra iii.4 “trayam ekatra samyamah”

“These three together – dharana, dhyana and samadhi – constitute integration or samyama.”
Dharana is to focus one’s attention on a point whether external, a spot on the wall, or internal the word ohm and to concentrate.  When the point of attention ceases to exist, when nothing else exist for the mind this state has become dhyana, or meditation.
Dhyana or mediation occurs when awareness of physical self, our body or the world around us, is fully absorbed within our consciousness.  When we no longer feel our feet, hands, etc., our minds are silent and all we feel is the energy of life.  This may manifest itself as calmness, a low humming sound, a vibration, maybe even a tingling feeling throughout the body.  Mediation is sometimes expressed as the merging of our true selves with the universe.  It is during meditation that samadhi is experienced.
Samadhi is known as spiritual absorption, union with, tranquility.  Samadhi is complete absorption and is experienced through dhyana or mediation.
Samyama is the trinity of the three, dharana, dhyana, samadhi.  Samyama is a process, a cycle where all three parts of this trinity exist and become one experience, samyama.  The progression begins with dharana and this concentration on something outside of ourselves brings us into ourselves and becomes concentration on ourselves, dhyana.  At some point we completely lose ourselves within dhyana and this is when we experience samadhi.  At this point samyama or integration is occurring.