¶ USB install medium
More info: https://support.apple.com/en-za/HT201372
¶ Older versions
¶ 10.10
This is an very old version of Mac. You can't install this version because the signing is not valid anymore. The software is perfectly fine. You will see the message:
This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading
There are a couple of solutions for this. You can disconnect the computer from the internet and change the date just after it's release. This will not always work. There's an other solution. Boot the installer and start the terminal. Run the next command. This will not check the signing but will start the installation.
installer -pkg /Volumes/Mac\ OS\ X\ Install\ DVD/Packages/OSInstall.mpkg -target /Volumes/YourDisk