Quite simply, this is the most important concept to embrace when beginning to learn hand and stick technique for drumming.
This is one of the first things we teach our beginning students who have never touched a stick before. Perhaps more interesting is that many drummers who have played for a long time do not know how to use these ideas.
So, this is a drum lesson for beginners, but many intermediate or even advanced players will benefit from looking into these notions.
Weckl explains his ideas pretty clearly, and you would be hard pressed to find a more credible source on hand technique than Dave Weckl, so please have a look at this video.