Systematic and meditative vinyāsa yoga practice
Ashtanga yoga is a systematic way of practicing traditional hatha yoga postures, where each posture is linked to the next one with pre-defined movements and breaths (vinyāsa). The breath is the central and most important element to the practice, coupled with a deep concentration inwards (pratyāhāra) during the whole practice.
The practice may seem like an acrobatic exercise, since we use our bodies to achieve these states of inner concentration and focus in hatha yoga.
When you start practicing ashtanga yoga, you will first learn the ujjayi breathing technique, inner activations (bandhas), and slowly start learning the primary series (yoga chikitsa), which is the first series of yoga postures (asana) in ashtanga yoga.
Led classes
Ashtanga yoga is typically taught in two ways: as a led group class and as a traditional Mysore style self-paced practice (see below).
A led class is what most people are used to when going to any modern yoga class or gym class. We all practice together in unison to the instructions of the teacher. This also means that the practice is more difficult to tailor to each individual student, but this is typically the easiest way to start your yoga practice, and this is also how most beginner courses are taught.
Mysore classes
In a Mysore style class everyone is practicing their individual practice independently, and the teacher is walking around and helping and teaching each and every one individually. This is the traditional way of practicing and learning ashtanga yoga, and is individual teaching in a group setting.
You learn little by little, and as you practice more regularly you will get new asanas added to your practice individualized to your physical abilities and needs. This means that everyone in the Mysore room typically has a different practice, and different length of the practice. Someone maybe practicing half of the primary series, while someone else practices the intermediate series, or full primary series.
As your breath becomes more smooth and you gain more control of your body, the teacher will start taking you further into the practice series, giving you new asanas one by one.