Both legs are placed behind the back and under the arms in shoulder extension. Besides requiring extraordinary external hip rotation and flexion, the practitioner should also have deep spinal flexion of the lumbar region and flexible shoulders. The practitioner should also have stable and supple knees that are properly conditioned so as to not be injured in the pose. 

Getting into Buddhasana with both legs is usually first done with somebody helping as I was in the picture above. Soon I will attempt both legs on own but after more experience practicing single leg and working to my maximum. One leg at a time is also much less complicated. 

One leg version of Buddhasana can be attempted if you already have a very accessible leg behind the head pose, called Eka Pada Sirsasana in Sanskrit by most schools. Start by doing leg behind the head and use your arms pressing your leg back as far as possible. See the video below to get the technique for getting into Eka Pada Buddhasana. One of the deepest "hip opening" poses. Keep the breath steady and relax as much as possible. Hip opening poses can certainly illicit emotional experiences coming from stored stress in deep tissues from recent or deep karmic memories.