How about starting with telling us what version of photoshop you have and what operating system your using?
Windows 7 photoshop CS5
Most of these tools can be applied to a new blank layer above your image. This will allow you to change your mind, or to reduce the opacity to reduce the effects of the tools.
Example when you brush out the dark circles under the eyes, reducing the effect by dialing down the opacity will bring back some of the original image, allowing the eyes to look more natural.
Most of the freckles can be removed with the spot healing brush, larger areas can be removed with the patch tool. Switching between the two tools will take care of most of your work.
Most important work on a back up image, that way any mistakes can be corrected. If your a beginner place the copy of the image in another directory, so you don't accidentally save over it.
And last but not least, have fun and play around with the tools, see what they do, then go to work.
Yes, using the tools of correction. Is available in Photoshop Cs3/Cs5.