Using the Quick Mask tool
Before beginning double click on the Quick mask icon near the bottom of your tool box and make sure that it is set as this illustration. The default colour is red but this can be changed to any other colour by double clicking the square and making your choice. Your alterations will remain in place unless you choose to reset them.
Choose the brush (or click B) from the tool box then go to your brushes palette. If this isn’t visible visit “Window” from the toolbar and tick “Brushes” to make it appear. Click on a medium sized (about 100) brush with soft edges ( the fuzzy edged icons) . Make sure that all the brush tip shapes are unticked as in this illustration. The size of the brush can now be altered to suit your image by using the square bracket keys [ & ] on your keyboard without fussing with the brush palette.
Now check that the default colour black is in place, press “Q” on your keyboard. The appropiate layer in the Layers palette will change to grey to indicate that you are in Quickmask mode. Paint over the area of your image you wish to work on. If you make an error change the colour to white (press “X” on the keyboard) and you can simply paint out your error. When your area has been fully painted press “Q” again and the red mask will disappear and the “marching ants” will appear around your selection and the layer will return to blue. Your Quickmask is now ready for use.