Avalon interface and Network on Chip Architecture, how are they related

You can't know everything about the insides of an FPGA anyway, so the question is rather to decide what information you need to know to do your job. In my opinion there should be very few cases where knowing how the NoC architecture actually works will be really helpful to an applications engineer. It is more useful to learn about the Avalon interfaces, how to create custom components and how to optimize a QSys design (http://www.altera.com/literature/hb/qts/qsys_optimize.pdf).