Well...I guess the best place to start about networking (like most subjects) is the beginning.
A network is two or more devices acting together in such a way so that at least one of them is getting something from the other that it couldn't get on it's own. (Note, that I did not say two or more computers hooked together.
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There are basically two types of networks- peer-to-peer (sometimes referred to as ad-hoc or workgroup) and server client. To be able to read this response, you will be experiencing both kinds of networks (and you didn't even know it until now). We are sharing information through our networks in a peer-to-peer fashion- I am posting this at my leisure and you will read it at your leisure. But, we are getting to it through a server client network. Our computers are requesting a service that they cannot perform themselves in order to do something, in this case, access the world wide web.
I mostly never deal with the first type of network.
Microsoft support are the people that do most of it, with an occasional repair person to let somebody that they need to replace some hardware. Workgroups or really only feasible for 5 or less computers and cannot function with more than 10 due to limitations of computer hardware. You will see them used most commonly in small office situations, or in someone's residence.
Okay, that's lesson 1.
I wish I could point you to a good book that provided an overview, or an online course, but there really aren't any. There are lots of resources on the web, but they are aimed for people who already know something about networking. (There's a similar phenomenon with Linux - a ton of stuff available, and almost all of it assumes that you already know how to use Linux, but at least there are some good books.) When I was starting in networking, the best book I could find (and sadly it wasn't one of my textbooks) was "Networking for Dummies"