Heading styles not only give your viewers a better visual representation of what the important points of your posts or pages really are, they also help search engines determine the important content on your site helping improve your visibility.
To create headings, make sure the post editor is showing the second row formatting options by clicking the Show Kitchen Sink button at the top right of the content toolbar. From here, you will see that the default styling is Paragraph. Highlight the text you would like to modify and then use the drop-down menu to select a different style.
By default WordPress offers six different heading styles for highlighting points in your content, or for separating topics on the same page. Heading 1 is usually the largest and most important incrementally scaling down for each of the following headings. When your content is formatted as you would like it to appear on your site, remember to save or publish your content.