I came across this on the Web:

"Html is simple because it is the exact document that is on the server,
all the server does is send you the exact document when you request it,
but php is a scripting language with html and it needs to be executed
before sent. This requires that PHP is installed on the server."

Does this mean that my Web hosting company must have PHP already
installed on their server, or do I have to somehow place it there?

I'm just starting out making a Web site, so I know nothing about all
this stuff.