The ring gives 8 manapoints and 2 hitpoints every 6 seconds on top of your normal regeneration rate for the 20 minutes that it lasts, which results in additional 1600 manapoints and 400 hitpoints in total.
There are many opinions whether life ring is more efficient than Ring of Healing, Manafluids or Mana Potions. You can check Money Spend Per Mana table where you can see a comparison of the different items that gives you mana.
You can get Life Crystals exchanged for Life Rings in the Gamel Quest. You can also obtain 1 of these rings from the Life Ring Quest and Behemoth Quest. A life ring is used in the Dreamer's Challenge Quest.