Monophyly is directly translated from Ancient Greek meaning "Of one race". Which simply means that your study includes ALL decendants. In the case of the diagram it means birds and reptiles back to a common ancestor. (yellow area)
Paraphyly translates as "near race". Which pragmatically means you only take into consideration only one branch of a particular common decendant including other related decendants. In this case, excluding birds. (blue area)
Polyphyly translates as "Many races". In this case you group them based on something other than an attribute of a common ancestor. In the case of the diagram it was actually "warm bloodedness". The common ancestor of both birds and mamals (both warm-blooded) was cold blooded. Therefore the attribute developed independantly at different times and in different ways. Therefore they bear no direct relationship in that sense, so they can be said to be "polyphetic".
How that relates to primates? Well, my interest lies in tracing the similarities and differences in the various ape species and learning how the different species tick. While I am "interested" in primates, my specific narrowminded aspie perseveration is learning specifically where and how each of the attributes in human beings evolved. And how they are different similar to other apes.
How did I get into it? Well, my first book that I really took notice of when I was learning to read was Origin of Species. Further research and following up the ideas lead me to evolutionary biology. I didn't care much about any other species but when I figured out (in a sort of final way) that humans evolved from distant ancestors I was "intrigued". I guess that's how I was hooked. Though why I was drawn to Origin of Species as a 7 year old I have no idea. I didn't understand a lot of what was going on in the book, but the instant I read it I wanted to know it all...