Queklain over at The Stoppable Force did a great post for me called Runic Power and You.
I was reading and tried not to be confused. As I was reading I was missing something VERY basic. Then I had my Death Knight epiphany moment.
You must spend your runes to gain runic power.
A death knight starts off with six runes to spend on their abilities. A death knight gets two unholy, two blood, and two frost runes to spend. This is unlike a rogue who has to create combo points to spend on their abilities.
When an ability calls for "1 blood" rune the death knight must have an available blood rune to spend. Once it is spent that one blood rune has a ten second cooldown. But there is a second blood rune available. Once that is spent also, the death knight has spent all available blood runes and cannot use an ability that requires "1 blood" rune until that first rune is off its ten second cooldown.
Using the two unholy and two frost runes are done exactly the same way as blood. Your runes give you a total of six abilities that can be used in a sequence in the ten seconds before the first rune is off cooldown.
When you use a rune for an ability it gives you runic power.
Each rune used gives you ten runic power. (The amount may change but at this time it is the case.) You can create up to 100 runic power (more with talents) to spend on additional abilities. This is unlike a warrior who has to create rage by being hit to spend on their abilities.
At this point Queklain's post made perfect sense.