As far as videos, Rodney Yee has some good ones. You need to start with beginning yoga, very gentle. People can get hurt trying to do what their extremely flexible/strong teachers are demonstrating. It's important to pay close attention to your own body and honor it's capacity.
After teaching hatha yoga for 20 years, I still occasionally injured my body when I would attend other teachers' classes. Because I am flexible, I would sometimes do something that I was capable of, but should not have gone into the poses that far.
I agree with C_sharp that real-life classes are the best way to learn the poses correctly and get a good introduction. (Just be careful and pay attention.)