A student needs to do a lot of horizontal threading so his concepts will be connected to similar concepts. In order to do this, he needs to look through his memory for things that seem related to the new information. An example of chaining or threading is finding common concepts or themes in history. If a student is discussing what is going on in Kosovo, for example, he might ask himself what the Civil War, the Holocaust, and Bosnia have in common with the current events in Kosovo. Meaning is making connections.
Connections are the concepts.
What Dr. McCarthy is saying is that in order to learn something, we need to understand its meaning. We make meaning by connecting new ideas to ones we already have. We connect them by their common concepts. Schema is a pattern or arrangement of knowledge that a person already has stored in his brain that helps him understand new information. For example, a student may have a definite image in his mind of what a reptile looks like by the information that he has been told about reptiles, by pictures that he has been shown, and by what he has read.