A barlow lens magnifies what an eyepiece can deliver in terms of magnification. You can get barlow lenses in different strengths, 2x, 3x, 4x, 5x, you can even get zoom barlow lenses! A 10mm eyepiece with a 2x barlow effectively becomes a 5mm eyepiece. Optical quality will suffer to some degree, since there's more glass in the path. As usual, less is more.
For photography, I'd recommend:
http://photography-on-the.net/forum
Whilst it's a Canon site, they're happy to accept other camera users and there's plenty to learn.
Hope this helps.
Dave