Ashtanga yoga,
Is one of the many ways, (Bhakti yoga, Karma yoga, Jnana Yoga, Mantra yoga, Tantra Yoga, Laya Yoga etc..) to reach the state of Evenness in Mind (Sthita Pragnya) and to  understand the true nature of ourselves. This "Eight steps to Yoga" method was structured by Maharishi Patanjali (Rishi means, One who has the comprehension beyond the senses  and has witnessed it first hand, where the knowledge of understanding is based on pure inner experience and not from any extenal aid. Maharishi is the one who has guided many to  the level of Rishi). We cannot date back when Yoga came into practice, but based on the Yoga science Texts we can come to an understanding that Yoga is in practice since the time  of  existence of the Life.

The Yoga practice is a Process of Simplification of a practitioner. Asana alone is Not Yoga, it is a part of the stages, Asana means a firm comfortable posture. A firm posture is very  helpful and needful for the practice, A firm posture is to be able to sit in a posture where the spine is erect for long periods without any pressure where the practitioner can forget the  state of body to dive deeper inside to experience the self. To be able to sit straight comfortably is possible only for a healthy body, which is why we practice different other Asanas to  make the body healthier. 

Saadhana, is the means that we accept to attain something. Ashtanga Saadhana means, using these steps to reach the Eighth Stage of Yoga - Samaadhi.

Ashtanga Vinyasa Yoga

Ashtanga Vinyasa Yoga is an Ancient Science of practicing asanas. Discovered through Yoga Korunta, and taught by Sri Tirumala Krishnamachar to their students.
There are Vinyasas (specific Movements) in every asana, and The Movements are Synchronized with deep breathing.

There are three main aspects of the practice, Ujjayi (Deep and even sound Breathing), Drishti (Vision point) and Bandha (energy lock).

Breathing : Deep Ujjayi breathing is done during the practice, A soft sibilant sound is felt behind the throat, which also contributes to create Heat within the body and burns the toxins in the form of sweat. The breathing also helps us to withdraw our sense of hearing from any external distractions we may hear .

Drishti : The vision points. In each asana there are specific places we look at, for being centered and also to withdraw our sense of vision from any external distractions we may see.

Bandha : The Locks within the body, the practice of Mula bandhaThe proper synchronization of Bandha, Drishti along with breathing

is held throughout the sequence. The practice of bandha has numerous effects on our subtle nervous system.brings

an uplifting energy for the practitioner, which makes the body feel lighter, thus making the movements more smooth, safe and effective. With regular practice, the practitioner gets a Feeling of "Moving Meditation" during the Flow.
With proper guidance, Almost anyone can take this practice and reap the benefits coming from it. A regular practice presents the practitioner with a strong, light and healthy body.

A practitioner must remember to not to be proud of their abilty to perform asanas or be disappointed for being unable to do an Asana, because there is no Absolute truth in Asanas, what is possible today may not be possible later, and what is not possible today can be possible later. Change is the only constant in here including our own bodies, our main focus must be in realising that which never changes, our self.