Never learnt it, was imbued with the power of shoppin by the Greek god Pan, to make woman lust over my imagery prowess.

same

learning by doing

Learn the basics of photoshop, then advance by following tutorials.

I started making sigs/tags using tutorials on www.deviantart.com . Found the hardest part was figuring out where everything is and how to adjust it to what the tutorial makers had used.. Most of them are really badly explained.. Youtube is also really good because they talk you through it.. Devianart also has a huge variety of basic photoshop tutes like photo editting etc.
Also joined a graphics forum and posted my work for cnc.. try www.planetrenders.net/forums most of them are pretty elitist but will still give you helpful advice

you lern it mate
use youtube and see some videos
not so hard