install El Capitan on external drive

[Emen Mali]

I'm trying to figure out what's the best way to get El Capitan onto an external drive (USB thumb drive) or actual SSD the MacBook Pro will boot from.

Right now There is no drive in the MacBook Pro (SSD) I am using Mojave on a Mac Pro 2009 but says I can't run the installer because its an old macOS. I've tried disk maker but keep getting errors.

 

[windrider42]

You can use a program called TransMac, if your running a Windows computer or Diskmaker X if on Apple