factory reset issues

I have been trying to do a complete 'factory reset' on a 2008 MacBook which originally came with OS X Snow Leopard - in order to pass it on to a new user. I had eventually upgraded to El Capitan & replaced the HDD with an SSD. I have successfully followed instructions to erase the disk & re-installed Snow Leopard, then moved on up to El Capitan, using my Apple id/credentials to sign in & download/install. I understand that I should be able to roll back via 'recovery mode' to a fresh install of El Capitan with none of my personal details but each time I try to achieve this I encounter problems at the macOS utilities stage. I get a message showing the hard drive & an exclamation mark & cannot go any further. I have noticed that when in disk utilities there are 4 entries (as shown in the attached photos). I understand that I should be erasing the actual disk which is the very first entry & not the indented one – or the lower ones. However in this view on another Mac I use, it only shows the actual SSD & then indented is 'MacOS'. Any help would be very welcome as I have now tried this several times with no success. I must be doing something wrong but not sure what, yet! Thanks in advance.