Using Quick Mask
Photoshop CS6 Tutorial
How to Use Quick Mask in Photoshop
Quick Mask lets you use the Brush tool to make a selection. Painting with white adds to the selection and black subtracts from the selection. You can also use the Brush tool Opacity settings to vary your selection.
Open an image in Photoshop (File > Open).
Make a rough selection using the Lasso tool.
Click the Quick Mask icon and note the color of the unselected area.
Choose the Brush tool (b key) and set the foreground color to black (d key).
Set the brush Opacity to 100% and adjust the brush size using the bracket keys ([ or ]).
Zoom in and paint with black to tighten the selection around the object.
Press the x key and paint in white to expand the selected area.
Once you are satisfied, click the Quick Mask icon to accept the new selection.