welcome!
also.. melvin the artistically challenged DM sounds like a childrens story.
you'll find tonnes of tutorials, tonnes of help, and tonnes of people here to help you...
My suggestion would be to dive in! a great way to start is to doodle on some graph paper, doesn't need to look great, and it's faster than trying to use a computer...
If your like me, you may also be interested in the mechanics of the thing.. when building a world, how does the geography work, when making a city, how do the logistics work, is there enough food available for a city of this size? hows the trade? how would that effect the people who live there... a mining town would be full of rugged dirty people... a frontier town would be full of ruff, hardy, tough, and probably rambunctious folk... there are tonnes of things to think of, and that detail is something i really like imaging when thinking up a town... it obviously flows out into mapping as well, approaching things modularly is a good idea.. take it one step at a time.. and ask for help! most people here will have at least thought of even your most outlandish ideas.. or most likely have run into a problem you have a dozen or more times.
we prop each other up with our knowledge around here.. that's why i love this place.