Here’s a practice that’s good for beginners. It’s fairly general, with some emphasis on alternately strengthening, then lengthening the hamstrings. The whole thing is around 22 minutes, a bit more if you do a resting pose at the end.
Even as this is appropriate for beginners, be aware that everyone has different restrictions and limitations. While the recording offers instruction, it of course can’t provide the in-person guidance of a teacher in your living room, so if you experience pain in any asanas, back off and explore how you might do the movement with more ease.
If pain persists, don’t continue to do what’s causing the problem and seek the advice of a qualified instructor.
The first part of this practice involves lifting the leg from a prone position in a few ways that may not be customary for some people. Being clear with these movements is less about generating a lot of effort and more about finding a fluid way to support what the legs are doing.
Keep in mind that you have a lot of latitude as to how much you lift the leg. If you feel discomfort in your back, you’re probably lifting the leg too much, putting excess leverage in your back. If this is the case, do less.