If you're interested in circuits (rather than programming) then I think it may be a very uphill struggle trying to learn only from forums or websites.
There is information dotted around the web, for example this PDF presentation on basic electronics but it's just a summary and you'd need to google the different topics in there to learn more. So basically you'd need to be prepared to research and self-learn a lot, and it could get frustrating.
However, there are some offline resources (books) which will make life easier. Forrest Mim's book is not bad. It doesn't have a lot of math, and so is easy to get into. It's easy-going, and has lots of practical circuits to experiment with.
This has nothing to do with the Raspberry Pi however. But, basic electronics will help with later understanding how to interface things to computers.
