In the Ashtanga system exist 6 series. Only a few people of the world are able to do all 6 series. The asanas are very demanding. Each series has different parts. The series start all with the surya namaskaras a and b. The standing poses follow. Then comes the middle part that varies from series to series. The closing sequence is again the same for all the series. Finally the yoginis can relax.
Most Ashangis struggle with the first two series. I did yoga for decades before I discovered Ashtanga yoga, but I thought I've never done anything with my body when I started with Ashanga yoga. The asanas of the Ashtanga yoga system are rather demanding. The vinyasas between the asanas make the series not easier. This might be a reason why there is so much focus on the asanas.
The series do not change much, but they've changed even in the last years. Some asanas were omitted (2 forms of paschimottanasna), others were added like urdhva dhanurasana in the first series.
In former times the first and the second series were taught almost simultaneously.
Nowadays first the first series must be performed correctly, including urdhva dhanurasana before the second series is taught. This evokes a lot of discussion and sometimes even dissatisfaction in the community. In shalas yogis are asked to stop when they are not able to do an asana, even though asanas follow that the yogi is able to do. Not everybody likes this.
I am too lazy to write more about the asanas. In addition I think the focus should be more the breathing. But me too I'm very much focused on the asanas. The challenge is to be patient. When a pose can be done, the next pose comes that cannot be done. And so it goes on and on.
When people say that they do yoga, they usually say that they do asanas.
There are series in other yoga systems, too. For a long time I did the sequence of Rishikesh.
More special for Ashtanga yoga are other parts: the breathing i.e., .......
.......to be continued.