Spelling errors and minor punctuation problems are nothing. An editor will find those and let you know what to do. Sit down and start writing. Related to the whole "writing" thing: http://www.youtube.com/watch?v=86x-u-tz0MA Ignore the dark and depressing parts
My advice is to just sit down and start writing. Take excerpts every now and then and see what friends or peers think. Hell, put it on here because none of us know you so we're more likely to be honest and not sugar coat it.