Photoshop is full of a wide range of tools and features, and a fair amount of them have some amount of overlap between their functions and capabilities. Two such tools are the opacity and fill sliders. If you are not quite sure of the difference between the two, this excellent video tutorial will get you up and running in no time.
Coming to you from Matt Kloskowski, this informative video tutorial will show you the difference between the opacity and fill sliders in Photoshop. If you have ever tried both sliders at the same time, it might appear that they function in the same manner, and that is actually true in a lot of situations, especially when you are simply adjusting the transparency of a normal layer. On the other hand, if you are using layer styles or a specialized blending mode, then the two tools do function in different manners. In particular, fill only affects pixels, shapes, and text on a layer in this case. Furthermore, when using the Color Burn, Linear Burn, Color Dodge, Linear Dodge, Vivid Light, Linear Light, Hard Mix, or Difference blending modes, they behave in distinct manners as well. Check out the video above to see the differences in action from Kloskowski.