In a class of yoga there are some exercises that you do with your body, that is your teacher will suggest you to do certain movements (for example, lift your arms, or bend forward, etc) and will ask you to coordinate these movements with your breath in a specific way. For instance, you may be asked to «raise your right arm, as you inhale».
You may also be asked to stay in a certain pose and breath a certain number of times...
The intensity of the exercises usually increases and by the end of the class it will start diminishing. The class can end with a relaxation (which can be guided or not, depending on the situation), or, when the practitioner's breath has achieved a good quality, the class can end with a breathing exercise, with a specific technique and/or rhythm.
A yoga practice, alone or with your teacher in individual or group class, is very personal. In other words, even if you are in a group with 10 other people, you should be focused on yourself.
We live in a world of competition and that usually conditions us. In yoga there is no competition with the others, nor with ourselves. Depending on the day, we can do (or not) some movements or poses comfortably; these movements or poses are not necessarily the same for someone else. It does not matter.
What really matters is how much aware of what you are doing you are, what you are feeling, how you are coordinating your movements with your breath, etc.
In yoga, it is better do a pose not so close to the standard one and being aware of the sensations of your body, than doing a very difficult standard pose and having your mind somewhere else, not your body or breath.
You can see the position of someone's body, but you cannot "see" where the mind is! So, don't get too impressed by the other's work... and if you are really flexible, stay focused on yourself!
One of the most difficult lessons in yoga is "to detach from the fruits of the actions". What does this mean?
Most of the times, we do something with an objective; if our action does not have the result we wish, we will be said or disappointed.
Practicing yoga produces endorphins, so it is pleasant, You should practice just to feel this pleasure. The results will come, but don't run after them, because that will not make them arrive faster. A regular practice, enjoying what you are doing and being as aware of your self as you can, is the best way to achieve the results you want.
In other words, respect your body! Many poses make certain muscles to stretch. This is very good, while you are working in a comfortable way. This means that you will fell the stretching, but you must avoid the pain. Remember, you are not trying to get anywhere! Knowing your body and breath requires concentration and learning.
Pain is the red light of the body! It means you are doing something you should not do, and it may have consequences. Latter, you may be able to learn how to tell the difference between different kinds of pain and learn which of them you can eventually work with. This takes a long time of practice and the supervision of your teacher. Otherwise you may end up with more problems than you had when you started.