The six fundamental postures are right at the beginning of every Astanga Yoga practice. No matter how advanced you are, after five rounds of Surya Namaskara A and B, you start with these postures. Here, you carry the rhythm you have set up in Surya Namaskara A & B in a flow from asana to asana. With this solid basis, you are perfectly prepared to enter whichever series you are practising.

Prasarita Padottanasana A Instructions
ekam
Inhale, step right foot back, feet parallel, hands to waist
Dhristi: to the nose (nasagre)
dve
Exhale, hands to the floor
Dhristi: in the middle of the eyebrows (bhrumadhye)
Inhale, lift head, extend the spine
Dhristi: in the middle of the eyebrows (bhrumadhye)
trini
Exhale, crown of the head reaches to the floor
Dhristi: to the nose (nasagre)
5 breaths, Prasarita Padottanasana A
Dhristi: to the nose (nasagre)
catvari
Inhale, lift head, extend the spine
Dhristi: to the nose (bhrumadhye)
Exhale, hold
panca
Inhale, hands to the waist, lift up
Dhristi: to the nose (nasagre)
Exhale, step to the front of the mat, big toes touch Samasthitih
Dhristi: to the nose (nasagre)
Prasarita Padottanasana B Instructions
ekam
Inhale, step right foot back, extend arms out
Dhristi: to the nose (nasagre)
dve
Exhale, hands to waist
Dhristi: in the middle of the eyebrows (bhrumadhye)
Inhale, lift head, extend the spine
Dhristi: in the middle of the eyebrows (bhrumadhye)
trini
Exhale, crown of the head reaches to the floor
Dhristi: to the nose (nasagre)
5 breaths, Prasarita Padottanasana B
Dhristi: to the nose (nasagre)
catvari
Inhale, lift up
Dhristi: to the nose (bhrumadhye)
Exhale, hold
panca
Inhale, extend arms wide
Dhristi: to the nose (nasagre)
Exhale, step to the front of the mat, big toes touch Samasthitih
Dhristi: to the nose (nasagre)
Prasarita Padottanasana C Instructions
ekam
Inhale, step right foot back, arms wide
Dhristi: to the nose (nasagre)
dve
Exhale, interlace fingers behind back (palms down)
Dhristi: in the middle of the eyebrows (bhramadhye)
Inhale, open chest, lift sternum, extend the spine
Dhristi: in the middle of the eyebrows (bhrumadhye)
trini
Exhale, crown of the head reaches to the floor, let hands fall over the head, reaching for the floor
Dhristi: to the nose (nasagre)
5 breaths, Prasarita Padottanasana C
Dhristi: to the nose (nasagre)
catvari
Inhale, lift up
Dhristi: to the nose (bhrumadhye)
Exhale, hold, hands stay behind back
panca
Inhale, extend arms wide
Dhristi: to the nose (nasagre)
Exhale, step to front of the mat, big toes touch Samasthitih
Dhristi: to the nose (nasagre)
Prasarita Padottanasana D Instructions
ekam
Inhale, step right foot back, hands to waist
Dhristi: to the nose (nasagre)
dve
Exhale, first three fingers wrap around big toes
Dhristi: in the middle of the eyebrows (bhrumadhye)
Inhale, lift head, extend spine
Dhristi: in the middle of the eyebrows (bhrumadhye)
trini
Exhale, crown of the head reaches to the floor, bend at elbows
Dhristi: to the nose (nasagre)
5 breaths, Prasarita Padottanasana D
Dhristi: to the nose (nasagre)
catvari
Inhale, lift head, straighten the spine
Dhristi: to the nose (bhrumadhye)
Exhale, hold
panca
Inhale, hands to the waist, lift up
Dhristi: to the nose (nasagre)
Exhale, step to front of the mat, big toes touch Samasthitih
Dhristi: to the nose (nasagre)
Prasārita Pādottānāsana A, B, C, D Benefits
Strengthens and stretches the inner and back legs, feet and ankles
Relieves upper body tension, elongates the spine and core
Develops the hamstring and abductor muscles (inner thighs)
Tones the abdominal organs
Increases digestive powers
Calms the brain and removes fatigue
Relieves mild backache