Before installing Mac OS X El Capitan 10.11.6, ensure your Mac meets the system requirements:
Unlike malware-ridden torrent sites, you should always start with Apple’s official servers. Apple maintains a support document (HT211683) specifically for downloading older installers. Mac Os X El Capitan 10.11.6 Installer Dmg Download
: Approximately 8.8 GB of available disk space for the installation. Operating System Before installing Mac OS X El Capitan 10