This is a great series of exercises to help your lower back and improve your posture.
Some of them are a little tricky, but take it slow and steady and after 12 minutes or so, you should definitely be feeling the benefits of being more limber. Over time, this will absolutely improve your core stability, posture and loosen up your lower back.
Do pay attention to the details and cues and continue only as long as is comfortable. If you have acute or chronic back pain, want to enjoy the benefits of better posture, or simply want to become a better athlete, this is a great posture improvement video.