When Private Browsing is enabled, Safari doesn’t remember the pages you visit, AutoFill information, and your open tabs aren’t stored in iCloud. Safari will also ask sites and their third party content providers (including advertisers) not to track you. Websites can’t modify information stored on your device, so services normally available at such sites may work differently until you turn off Private Browsing.
Note: While Private Browsing is enabled, the Safari user interface appears dark instead of light.