Well I, in my infinite ignorance managed it.
https://github.com/retropie/retropie-se ... stallation
My first attempt was by downloading the SD image. Then I followed the detail I found after a short search to install RetroPie onto a new-ish Pi3/8 Gigbyte SD installation. I can't be sure the above is the same one but worth trying. I did take quite a while.
I found I had to go buy a USB XBox360 controller and got one from (UK) Argos for 12 quid (special offer) and it seems necessary to control/setup/run EmulationStation's emulators.
The only problem I have had was with configuring the Xbox controller's button mappings, it would always skip a control button. Using the EmulationStation set up menus I reinstalled/updated the Xbox drivers and it now works OK.
Clearly there was enough detail available on line for me to get it going. My daughter's little lad is very happy playing the Amiga games his mum once played. So, its all do-able for an over-60. (that's a challenge)
Share and Enjoy.