Because this download is an packaged disk image containing an installer payload, you cannot simply drag it into your Applications folder. Follow these steps to extract the actual application. Step 1: Extract the Installer Package
Method 1: The Official Apple "Fixed" Installer (Recommended)
Press Enter, close Terminal, and restart the installation process.
This process does not install the OS; it extracts a file named "Install OS X El Capitan.app" into your /Applications folder. This 6.2GB app is the actual tool you need to upgrade or create a bootable USB. Step 3: The "Expired Certificate" Fix
shasum -a 256 /path/to/your/download.dmg