So far we haven't said much about the mechanics of writing sentences and paragraphs, nor is it really within our scope to teach those skills. But the proper use of grammar and spelling are crucial far more so than you might think, especially in a time when more and more people seem to ignore rules of spelling and capitalization in e-mails, and even the daily newspaper all too often has spelling and grammatical errors.
Why? Isn't it the story that counts, not whether I spelled the words right? Lots of people make mistakes. What's the big deal?
The big deal is that every mistake you make whether it's getting a verb tense wrong, or mangling a spelling, or using a word incorrectly distracts the reader from the story and undermines all the hard work you've put into casting your spell. It also undermines the reader's confidence in your thinking and skill, and thereby her trust in the story. Always be careful, and use the dictionary or the spellchecker when you're not sure of a meaning or a spelling.
If you need help in particular areas, here are some places you can turn: