Savasana (corpse pose) is a resting pose that is usually used at the end of yoga practice. But you can use savasana at any point in your practice to integrate the movement and practices you've done.
Savasana helps us to let go at the end of our practice. It helps to calm the mind and induces a sense of relaxation. You can also use savasana throughout your day as a way to "reset", process daily events, and reduce fatigue.
As you set yourself up give yourself time to release any areas of tension and fatigue. Lay the body down, align the skull, sacrum, and spine. Bring your arms away from your body and invite your legs and feet to drop out towards the sides. Consciously relax the body and breath.
There are many ways to practice savasana, but the most important thing to remember is to find a position that is very easeful. I recommend using a timer so that you can totally let go while in the pose.Try to practice this pose on your mat (not in your bed) to establish this pose as something other than nap time :)
If lying on your back is uncomfortable you could practice this pose on your side or on your belly. You could support under the knees with a bolster, use sandbags at various places on the body and use an eye pillow. If the chin is rocking up towards the ceiling its best to support under the head with a small folded blanket.
Remember this is a really important pose. Give yourself enough time to really sink in!