Hi
I'm new here, thought I'd try and help. As others have said there are a lot of photo editor's out there, some free some not. GIMP is free and fully featured, but you can do a lot without it being to technical.The software's available here http://www.gimp.org/downloads/
There's various tutorials available on how to achieve different effects, a lot of them on youtube. For instance a google search on "skin retouch with gimp you tube", gave this vid http://www.youtube.com/watch?v=EMaV5h9MH1s .
So with some google searches and some time you can achieve quite a lot
If you feel you can't achieve what you want with the software then you could always contact me see post here ;
http://www.saafe.info/main/index.php?topic=2811.0
Hope that helps a bit