Start by logging into the backend of your site, by going to yourdomain.com/admin, and log in by entering your username (email) & password and you're in. Once inside the Content Management System, you'll see a long set of navigation buttons on the left side.
Click Modules, and then click Blogs.
Click New Post and write the post. Remember to give your new post a Post Name.
After you're finished writing your new Post click Update. Your New Post is now live and on the Blog Page of your site.
If you want to publish your post in the future, set the Release Date to the future date and click Update.
To prevent Spam be sure to Uncheck the box next to Enable Comments.