A quality VPN will prevent you from being tracked through it since your IP address will be hidden from the sites you visit. However, there are other ways that you can be tracked online, some of which will function even if you are using a VPN. If you are logged into Google or Facebook while using the VPN, those companies may be able to see which sites you visit regardless of whether your VPN is on or off. In addition, if you click on an ad while using the VPN, that ad may employ tracking technologies that a VPN cannot block.