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gojsawyer eNotes educator| Certified Educator
In formal writing such as essays and research papers, a header is a location at the top of the pages of the work that gives basic information about the paper. The information in a header usually includes the author’s name, the name of the recipient (the professor, the publication, etc.), the date, and the page number. Different styles exist for the formatting of headers in formal writing. The Modern Language Association (MLA), American Psychological Association (APA), and Chicago Manual of Style are among common styles for formatting headers and other aspects of formal writing. It is best to consult these sources either on their websites or in their printed style editions for the most updated standards for writing headers. In general, one style will be used throughout the paper, not a mix of different styles.
Chris Curtis eNotes educator| Certified Educator

The header is the very top of the page and is the partner to the "footer."

In Microsoft Word 2007 you'll find it under the "Insert" tab. An easier way, though, is to simply double-click at the very top of your document. It will show a dotted dividing line with a tab that says "header."