Malasana, a great hip opener
This is one of my all-time favourites :-) Oh, hang on, I say that about almost every yoga pose I do, ha ha. Malasana, also known as Garland Pose is a great hip opener. I personally prefer it's Spanish name - la rana - which means frog.
It relieves tension in the lower back if you can open your hips sufficiently and relax in the pose (warning: it can be really hard work if you aren't used to hip-opening poses).
You need to stand with your feet quite wide apart and squat. Your toes should be pointing outwards. Make sure your knees don't go past the tips of your toes, keep the arches of your feet active and don't let them roll inwards, keep your back straight, and try to align your elbows with your wrists, joining your hands together in Anjali Mudra (prayer position). You can use your elbows to push back on the inside of the knees, to help open a little wider. Relax your lower back, giving into gravity, as if you wanted to sit down on the mat. If you are familiar with Uddiyana Bandha, apply this now. Hold for as long as is comfortable.
As you become more experienced, you can try bringing your feet closer together.
Tips in case of difficulty:
1) Increase the separation between your feet.
2) If your heels don't touch the mat, place a block or cushion underneath them. You can also roll the edge of your mat a bit and use that as support.
Send me a message if you are experiencing other difficulties that I haven't mentioned, and I'll try to give you some pointers.