The red arrow is pointing to the (a)   mode menu. (Blend, Layer Mask)

The (a)   panel displays the layers names, and thumbnails of the content of each layer. (Tools, Layers)

Organizing your layers is important, create a new layer (a)   to keep similar layers together. (Mask, Group)

To adjust the Brightness/Contrast of an image, use the new (a)   layer tab. (Adjustment, File)

The layers (a)   determines how transparent the layer will be. (Visibility, Opacity)

The red arrow is pointing to the tab that makes a new (a)   . (Group, Layer)

The Layers panel (a)   gives you options such as quick exporting, delete layers, merge layers and more. (Menu, Lock)

(a)   in Photoshop are used to separate different elements of an image. (Layers, Tools)