What is the exact model of your Mac and the version of macOS you are using? You can get this information by clicking on the Apple menu and selecting "About this Mac".
If you are running an older version of macOS, then Safari may be out of date. You may need to use a third party web browser such as Firefox (only macOS 10.12+), Google Chrome, or Vivaldi. Apple only updates Safari for the currently supported versions of macOS which are currently macOS 10.13+. Once the next version of macOS is released sometime in the next few weeks, then macOS 10.13 will stop receiving security updates.