Welcome, Xanthia ! Do you know what kind of look (and what kind of planet) you're after? Do you see any of the tutorials that are along the lines of your goal? If so, fire one up and take a stab at it ... while you may be facing a sudden need, you may be happier long-term if you fiddle around some, and go with your third or fifth attempt. We'll be glad to help you along, if you'll post your efforts in a work-in-progress thread as you go.
Do you already have some graphics software at hand? Or are you looking to tackle this world with pen and paper?