Not to threadjack, but I find that I always use an adjustment layer. I like being able to trash the experiement without going back to square one, or even reverting to a previous saved copy.

As for the Curves dialog it's mostly based around how the line is shaped and interacts with three points along the line, Black, White and Middle Gray. Think of it as a graph of how you want to adjust the contrast and brightness of the image.

Just want to make it brighter? Simply click the middle of the line (middle gray) and drag it higher in the "graph". This will cause a shift to make more shades the lighter side of middle gray. Similarly you can cause curves in the line to force the shades near the ends to compress, making more white or black areas, thus increasing the contrast between the two.

Then again after 3 years as a graphic designer, I still manipulate the curves dialog box in my dreams.