Sankhara conditions vinjana dependent origination

When it is said in dependent origination that "sankhara conditions consciousness", in what way and how does sankhara condition consciousness? And also, how is consciousness conditioning nama rupa? And then nama rupa conditions salayatana again how? Also, nama rupa -- I have heard many different descriptions of what it is, so i would be happy if someone could give the right meaning of nama rupa. Going back to "sankhara conditions consciousness", what consciousness are they refering to -- is it the pure consciousness or limited consciousness? And how can avidja or ignorance and sankhara come before consciousness in dependent origination (because i must first be conscious before i can have ignorance and do sankharas!)?