Yoga is about baby steps, we must crawl before we can walk and walk before we can run. Ask the instructor for a modification if one is not offered. Every single one of us is unique and no two people will ever do a pose the exact same way.
If you are finding something particularly difficult or just don’t feel like doing that particular pose for whatever reason, come into a resting pose like childs pose or savasana and wait for the next pose to be introduced.
Yoga asana is not a competition, let go of the ego and really tune into the needs of your body, make the practice your own; honoring your body and doing what is best for you, not forcing yourself into a shape that you aren’t ready for, or maybe will never be ready for because your unique anatomy does not allow for it.
Everyday is different and what works well one day may not be accessible to you the next. Be prepared and willing to adapt to the changes, be kind to yourself, release your ego and listen to your body. Then you are truly practicing yoga.