Welcome to the fourm.
I hesitate to suggest posting on one of the forums. Perhaps post a couple of paragraphs so someone can see what you are doing wrong.
However, some suggestions: First, try reading it aloud to someone. Often doing that will show up errors of syntax/grammar. Second, make sure your capitalizations are correct. Third, make sure your tenses agree and that your pluralizations agree with the verbs.
Grammar/spell checks often cannot identify as wrong the misuse of words - if a word is spelled correctly, it will be shown as correct but be the wrong word in the context.