This group has quite a lot of forums about the theory, often goig several moves deep, we also have a professional chass coach who will answer your questions about the scotch for free.
Understanding opening theory...
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It wasn't specifically about opening theory, but I found reading through Chernev's Logical Chess to be very helpful in understanding some of the key concepts behind the openings and seeing how masters formulate their plans in and after the opening stage. Of course it also goes beyond openings, which is great. I found a copy at my local library, so you may be able to read through it for free as well.
Thx Ronis, I didnt know youtube had videos? I'll have to check them out! And I agree with you Ian, this site is great for learning oopenings and many other things, I had a premium membership for one month and I learned a lot from here:)