For a simple guide on how to stretch prior to or after exercise see Netfit.co.uk.
If you want a really in depth guide to stretching see Bath.ac.uk
Stretching has many benefits eg :-1. Improved flexibility.
2. Improved circulation.
3. Improved posture.
4. Improved balance and co-ordination.
5. Helps one relax.
6. Can reduce lower back pain