There are definitely all sorts of yoga teachers and classes out there. There are people who like the astrology/mystical stuff or mixing in some religion or another, and I guess I feel like whatever gets people to exercise, to move mindfully, to take care of themselves, I'm glad it's there for them. Like Bounceswoosh, I also enjoy the setting intentions, the "Om's", focuses on alignment and anatomy, and personally I like learning sanskrit pose names and the stories behind them - which does incorporate some Hindu stuff, but to me there is a big difference between, "this pose is called Hanumanasana, after the story of Hanuman's leap from Sri Lanka to the Himalayas, so you can visualize the full splits while leaping..." Which to me is like... interesting factoids, not "let us pray".
Some of the classes I go to have opening and/or closing chants in Sanskrit. Again, I find this interesting to learn about, but do understand that not everyone is interested in that. The teachers I go to always preface it with that all of the chanting is optional. But if that would bother you, avoid Ashtanga or Anusara classes, where it's traditional.
But DEFINITELY don't feel pressured to keep up with anyone in any class, or to do any pose that just isn't working for you (things should feel like reasonable exertion/a "good" stretch/something you can continue breathing deeply while doing - if not, slowly back out of it.) For instance, your legs might shake and your muscles might burn like crazy in chair pose, and that's good, but joint pain would be bad, as would needing to hold your breath. Most teachers will say that you can always rest in child's pose, at a minimum, and a lot are even more flexible and encourage you to do whatever variations you want to do. (The downside is that it can be confusing as a newbie if everyone is doing something different to even figure out what the pose IS that is being talked about!) But as you gain more experience, it's easier to say oh - pigeon pose - my back doesn't like that right now, so I'm going to do a reclining figure 4 today instead. If they are going into a pose which just isn't going to happen right now, it's okay to look around and see if people are doing more accessible variations. This also is a good signal to the teacher that you're looking for an alternative and they can offer something too (if you just go straight to child's pose, the signal is that you want to rest). The key is to not get stuck comparing yourself to others. We all have different genetics, different injuries... and no one is a better person because they're flexible. In fact, yoga is much harder to do properly for people who are very flexible - it takes a lot more muscle and willpower to hold alignment properly when the body just wants to collapse. Everyone has their own challenges. I do find that when I focus on form, yoga helps me find a nice balance of strength and flexibility, and it's really helpful in sports.
Oh - also note that at first, some people have a really hard time with things like savasana, which is the lying on your back and resting at the end of class. Some people are more fidgety, or just have too much going on in their heads for it to be relaxing at all, but I swear to you it gets better with time and practice. I know years ago I would regularly swear that the teacher left and was leaving us in savasana as a joke/torture, but now it goes by in a flash. So it's not abnormal at all to find yoga stressful instead of relaxing at first. But stick with it!
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