Although you can begin your yoga practice just to satisfy your general interest in the physical aspects of yoga, eventually you will want to learn more about it. So, let's begin.

What is Yog (yoga)?
The meaning of yog is derived from the sanskrit word "yoj", which in English we know as a yoke, which is an instrument which unites two different beings (horses) so that the two entities continue in the same direction. Each of us is made of two aspects, the minds and the body. When these two aspects of our being are out of alignment, we would say you are out of "yoj". The object of "yog" is to bring these two diffect parts of our being into harmony. 

How do we do this? By combining two forms of yog, Hatha Yog, which works on the body, and Raj Yog, which works on the mind. This is known as Ashtanga Yog.

So, what is Ashtanga Yoga?
In short, Ashtanga Yoga is the combination of the 5 disciplines of Hatha Yoga and the 3 meditative states of Raja Yoga. Combined, these constitute the 8 limbs of Ashtanga Yoga.

HATHA YOGA: (physical control) 

YAM (yama): (5) Social Disciplines (how to live within the world) 

1. Nonviolence (word, action and thought) 
2. Do not steal 
3. Release of envy (possessions and accomplishments) 
4. Speak and live TRUTH 
5. Practice self-restraint (do not live in excess or depravity) 

NIYAM (niyama): (5) Personal Disciplines (how to live one's life) 

 1. Maintain mental purity and physical cleanliness 
 2. Rise above objects of desire 
 3. Accept your situation in life 
 4. Repeat the sutras 
 5. Devote yourself to a personal diety- or the universal consciousness 

ASAN (asana): (Bandak, Mudra) physical poses, postures, that help create a sound body and mind (asan = posture, being) 
PRANAYAM (pranayama): control of your breath (prana=life force, yama=control)
PRATYAHAR (pratyahara): control over the five senses (you do not let yourself be led by the desires provoked by the five senses)

RAJA YOGA: (meditative) 

DYANA: 1st Stage of Meditation. Concentration: development of conscious awareness
DHARANA: 2nd Stage of Meditation: Contemplation: deep reflection and meditation 
SAMADI: 3rd Stage of Meditation: Enlightenment: complete sense of oneness with self, universe and environment through deep meditation. Release of ego for universal self.