Photoshop Help

You can search how to use certain tools in the help section of the Adobe website. The link is: http://help.adobe.com/en_US/photoshop/cs/using/index.html

You can enter something in the search bar but make sure to check off "this reference only"

For example you could search for: retouching
The results will direct you to information about retouching in Photoshop, what tools to use, and what the different options mean.

Here are some links for you.

Cloning
Healing
Layer Blending Modes
Quick Mask Mode
About Layer Masks
Adding a Layer Mask