1. Login to your dashboard and then go to Appearance and then Menus
2. Select a menu to edit from the drop-down shown above and click select.
3. Click on Page or Post and then put a check mark next to the page or post you would like to add and then click on the Add to Menu button. You can drag and drop the new button wherever you would like it. If you indent it under another button it becomes a drop down.
If you are wanting to add a custom link, for example, a link to another website or a PDF file copy the link and paste it in the URL and then type the button name in the Link Text area.
4. Make sure to click on the blue Save Menu button once you are done.