Clicking on the arrow below the header icon opens the drop down menu showing the built-in headers that you can scroll through to see if there are any you would like to use. These are set up with spaces allowing for titles, dates, page numbers, author name, book titles, etc. Some also include graphic elements such as lines, circles, blocks and colors. These are already formatted. If you find something you like, select it and then all you need to do is type in your information where indicated.
Once you select a built-in header, whether it is a blank one or pre-formatted, it will open at the top of your page and the Header & Footer Tools tab will open allowing for changes to be made. Some of the built-in headers when chosen will also open the Table Tools tab where the header can be modified further by selecting table styles.
The design options under the Header & Footer Tools tab include the built-ins and inserting date & time, quick parts, pictures & clip art. You can also navigate between header and footer and sections of your document. There is the option to have a different header on the first page and also different odd and even pages. Margins from the top for the header or bottom for the footer can be changed as well as inserting tabs. Not all the options are available for all the built-ins.
Inserting page numbers works the same way. This option is the one to use if you only want page numbers on your document. Clicking on Page Number opens the drop down menu offering to insert numbers at the Top of Page, Bottom of Page, Page Margins or Current Position of wherever your cursor happens to be, including the middle of the page. For each above option that is selected, produces a menu of layouts to choose from. This includes placement and added graphic elements. There is also the option to Format Page Numbers allowing you to choose numbers, letters, Roman numerals, and section or chapter numbering.
Any time you want to change your header, footer or page number or remove them, you can find those options at the bottom of each respective drop down menu.
The last option listed on the header and footer drop down menus is Save Selection to Header (Footer) Gallery. This is where you can create a custom header or footer in your Word document, highlight it and then make this selection. You will be prompted to give it a name and you can choose which gallery to include it in and a description if you want. In the image below, I inserted a flower image, followed by my name and then I inserted a page number in the current position. After choosing the font and color, everything was centered and a line was added. Then everything was highlighted and I selected Save Selection to Header and named it. Now, I can select this header from the list of built-ins anytime I want to use it!