Select the layer you want to mask
Click the Add Layer Mask button in the Layers panel
Use a black brush to hide parts of the layer
Use a white brush to reveal parts of the layer
Press X to switch between black and white
Use the Brush tool with a soft edge for smooth transitions
Use the Gradient tool on the mask for gradual fades
Use Select and Mask to refine complex edges
Use the Properties panel to adjust mask density and feather
Alt-click the mask thumbnail to view the mask directly
Shift-click the mask thumbnail to disable or enable the mask
Link or unlink the mask from the layer as needed
Paint on the mask with gray to create partial transparency