If you're just starting with shooting portraits and retouching them, learning and subsequently mastering the myriad of techniques used in Photoshop can be a bit daunting. This helpful video will get you up and running.
Coming to you from Anthony Morganti, this tutorial runs you through his process of retouching a portrait in Photoshop. Portraits take a nuanced eye and touch: too much or imprecise retouching can lead to an artificial-looking result, while too little can lessen the impact of your work. While there are a veritable multitude of ways of removing blemishes, whitening teeth, and the like, Morganti's workflow is a great one to follow for beginners and will help you better understand the things you need to pay attention to to create realistically retouched portraits. Also note that Morganti uses a Wacom tablet; I definitely recommend picking one up if possible. You'll likely find the natural motion of drawing on a surface to be much more conducive to precise work than a normal mouse or a touchpad.
And if you'd like continue learning the basics of photography, be sure to check out "Photography 101: How to Use Your Digital Camera and Edit Photos in Photoshop!"