To answer your "fundamental" question: Yes. This only applies when you are playing a game of High/Low, such as Omaha High/Low, where the high hand takes 1/2 the pot and the low hand takes the other half. First take the five cards that make the best high hand, and then take the five cards that make the best low hand and yes, you can use each card once in each hand.

Welcome to the PFO.

__________________
If you feel you have a question, dont be lazy; make sure you have asked yourself first. Then search the forum, then just fucking google it to get as much detail as you can. You may then seek clarification on specific points from others.