Look around through the forums, see what people have done that you like, then take a look at the tools they used to get there. There's a pretty good chance that there is a tutorial to at least get you close to anything you like. Ascension's satellite style is quite popular, and the Zombie Nirvana tutorials on YouTube are also a good place to start with Photoshop.
There are tons of tutorials in our tutorials section devoted to Photoshop, and most of the authors are more than happy to offer advice if you run into trouble.
Most of all, start a Work in Progress (WIP) thread. You'll get the highest quality advice from showing us exactly what you're doing, even if you're starting with nothing more than a silly-looking block drawing. And don't worry about where you are right now; talent isn't as significant as effort!
Welcome to the Guild, and enjoy!