An adjustment layer will apply color and tonal adjustments to your image without permanently changing pixel values.Instead of making Level or Color/hue adjustment directly to an image you can create the adjustment layers for each.  The color and tonal adjustments are stored in the adjustment layer and apply to all the layers below it; you can correct multiple layers by making a single adjustment, rather than adjusting each layer separately. If you wish to discard your adjustment ,you can always do that anytime.

Adjustment layers have many of the same attributes as other layers. You can adjust their opacity and blending mode, and you can group them to apply the adjustment to specific layers. Likewise, you can turn their visibility on and off to apply or preview the effect.

Fill layers on the other hand, allow you fill a layer with a solid color, a gradient, or a pattern. Unlike adjustment layers, fill layers do not affect the layers underneath them.

To apply and adjustment layer:

  • Click the New Adjustment Layer button  at the bottom of the Layers panel, and choose an adjustment layer type.
  • Choose Layer > New Adjustment Layer, and choose an option. Name the layer, set layer options, and click OK

.To apply fill adjustment layer

  • Layer > New Fill Layer, and choose an option. Name the layer, set layer options, and click OK.
  • Click the New Adjustment Layer button  at the bottom of the Layers panel, and choose a fill layer type.