Welcome to Chinese Medicine.... not everything here is linear certainly. In very general terms you can think of qi as your day to day energy from food, kidney yin and yang as your savings account and jing as a trust fund. If you have a poor day to day lifestyle and don't supplement your qi (your checking account). To supplement your checking account your body will pull from the kidney system (yin/yang) (your savings account). And if you run it all dry through illness or very poor lifestyle or simply through the aging process you tap into your trust (the jing). When your trust is gone, you have nothing else to fall back on.
In general jing is the deepest energy we have, the spark that lets us come back from very low places and that which provides the magical component of fertility, etc. The general theory is that we are born with a certain amount of jing and when that is gone we are gone. We prolong it's levels by maintaining proper yin/yang balance and supplementing our qi.
For more basics, read "My Kidney's Are What?" and possibly look through common kidney disharmonies to see the depth differences between yin deficiency and jing deficiency for example.