Thanks Ralph. That video was particularly good. But I don't seem to have missed any steps.
MAMP seems fine. I can open the Start page, I can do the PHPinfo page, I can create a database in PHPMyAdmin.
But if I create a index.html with "hello" in it and put it into MAMP/htdocs/index.html I get: "The requested URL /MAMP/htdocs/ was not found on this server."
Similarly WordPress doesn't work.
I preferences for MAMP I have:
Apache port: 8888; MySQL port: 8889
and the URL is http://localhost:8888/MAMP/htdocs