We can customize the navigation on SharePoint sites by managing the Quick Launch bar and Top link bar. This allows adding, removing, or editing links to help users easily access lists, pages, and other parts of the site. The Quick Launch bar appears on the left side and displays links in a logical manner, while the Top link bar is similar but appears at the top. We can add new links, change the order, and configure navigation settings to control whether these bars are enabled and how the site content is displayed to users.