Do I need prior experience?
Absolutely not. Yoga is a practice which welcomes everyone no matter what their prior experiences are.
I am not flexible, is Yoga for me?
Absolutely yes. Flexibility is irrelevant to practicing yoga. If you are flexible...great, if you think you are not...great too! The regular practice of mindful movements can help towards achieving more flexibility (if this is what you are looking for).
What is Yoga?
Yoga is a practice which comprises of different tools and techniques (meditations, breathing techniques) which allow you to connect your body and mind with your surrounding, with the objective to become one. This is one explanation...I can also offer you others. I can use other words and get you to visualise other situations depending on what resonates with you. However my advice is try it and see it for yourself. "How do you feel at the end of your practice?"