What is Concrescence?
...it is a moment of experience....
The video above introduces you to Whitehead's idea of concrescence. It is one of seventeen lessons offered in What is Process Thought? Taken as a whole, and in combination with other sources, the videos can help you read and understand Whitehead's Process and Reality.
But process thought is not just about Whitehead. It consists of twenty key ideas that are shared by process thinkers. See What do Process Thinkers Believe? Not all these ideas mean the same thing to people, and other people might come up with different lists. For example, if you are curious about what process thinking means in China, and links between Chinese thinking and Whitehead's philosophy, see Comparing Whitehead and Chinese Thought and Why Process in China? It's a Lifestyle.
Perhaps most importantly process thought consists of the personal and social implications of process thinking. See World Maps for World Loyalty and Our Ongoing Influence in the World and Replanting Yourself in Beauty, or Suffering and Meaning: Reflections on a Death and God and the Sendai Earthquake.
A good website to consider the entire range of process thinking might be JJB and Process Philosophy and the Culture of Possibility.