Seated Wide Leg Hamstring Stretch
For beginners or people with tight hamstrings, this stretch can be made easier by sitting in a chair.
To go deeper in seated wide leg forward fold (Upavistha Konasana) learn first how to activate the hamstrings to control your descent. Then learn to relax them so that you stretch them. Also, learn how to add weight gradually to deepen the stretch to the hamstrings.
The goal in each of these steps is to increase flexibility.
The first set of exercises trains you in activating the hamstrings. Once you can feel when your hamstrings are active, and once you can deliberately activate them, it is then that much easier to keep them relaxed so that you can stretch them.