One of the best ways to learn is just to simply sign up to a couple of computer forums and read all the latest posts/threads.
Another way that I learnt a lot was by building a computer. Of course you don't need to build a computer, but you could pretend you were going to buy all the parts. In which case you'd need to think of what you need (e.g. Case, CPU, GPU, PSU, Motherboard...)
And if you still want to learn more, then here's a quick list (off the top of my head) which you can research online;
• Overclocking (CPUs, GPUs, and RAM)
• SSDs vs HDDs - Pros & Cons
• Water-cooling
