At what level do you want to understand things? I feel that getting the basics is best done by trying it out yourself, though a badly configured public server can be used to attack other people, so be mindful of who has access to your server when you're trying things out. If you just want the theory, Wikipedia is a pretty good resource for technical things.

If you just want to see how DNS works, set up a server yourself. You could start with a simple caching one like unbound, and then get yourself a domain and set up a real server (eg. nsd or bind) for that. You could for example use Hurricane Electric's free DNS service as your main nameservers and make use of zone transfers and notifications to keep things up-to-date from your local server, giving you a small-scale "real-world" DNS setup.