Several years ago I came across an excellent educational website on complexity--at a time when few such websites existed. In the late 1990s you basically had the Santa Fe Institute Website and a few other things.
Then came along CALRESCO, which stands for the Complexity & Artificial Life Research Concept for Self-Organizing Systems. If you typed on Google or any other web browser words like "complexity" or "complex systems" the top hit was from CALRESCO.
Now, Wikipedia dominates, which is a good thing. Survivial of the fittest! However, the drawback is that an excellent educational website is getting less attention.
What makes CALRESCO so good is the level of detail. When I was first learning the numerous concepts of complexity science, CALRESCO not only provided excellent information, but it had lots of papers I could download to read, and they were at a basic level without being basic--does that make sense?
Anyway, if you want to get a good grasp on the basic cocnepts of complexity science, I recommend making this part of your favorites list.