Welcome Steven. There are a small handful of planet related tutorials available here but honestly your best bet would be to do a search for planet tutorials over at Deviantart, there is far more available there. As to world map tutorials, we've got that covered. We've got maps tutorials in several styles for all sorts of different software. Some people use FT3 (Fractal Terrains) to create world maps and then pretty it up a bit in Photoshop or GIMP. I've never used the software myself (it is not free and I'm poor student), so I couldn't say how steep the learning curve is. By far the most popular forms of software here are Photoshop and GIMP. They are both very versatile and a majority of the tutorials submitted here are for one or the other of them. I use GIMP because it's free, but would use Photoshop (CS not Elements) as well if I had it. So if you have one of these software programs best to start there. If you have neither, download GIMP for now and you can always upgrade to Photoshop down the road.
Next, spend some time browsing the tutorials section. In particular, check out the "Tutorials in PDF format" sticky in that forum, since tutorials are grouped by software program there. These will help ease the difficulty of learning a new program and you may be surprised at what you are able to accomplish. Then, once you've begun a project, start a WIP thread so as to elicit constructive feedback from more experienced Guild members. Soon enough you'll be creating maps.