Continuing to refer to the Layers Palette above:

Link between Adjustment and Mask: The Link between a 'thumbnail' and 'mask' ensures that the two parts work in register (this applies to any layer with a mask, Layer Mask, etc). If needed the 'link' can be disabled and the mask allowed to float free - yes there are occasions when this is useful.

'Eye' icon for Layer Visibility: Clicking on the Eye' icon will turn on / off the layer thus making it visible or invisible.

Layer Lock Options: It's sometimes helpful to 'lock' a layer to inhibit or prevent further changes. The locks provide a selection of facilities: left to right: 'Lock Transparent Pixels'; 'Lock Image Pixels'; 'Lock Position'; 'Lock All'.

Blending Modes: By clicking on the drop-down arrow to the right of 'Normal', a list of 'Blending Modes' appears. The choice of 'mode' determines how the layer above interacts with the layer beneath.