URL Related Question?

[J]

the current answers so far are too complicated.

as you know the html and php extensions are how the server decides to compute your page,

html of course is just displayed, but php is acted upon by the server.

if you need php code on an html page, normally you would tell the server by the ending php extension

HOWEVER, you can tell the server to treat html extensions as if they contained php and to execute them as php WHERE IT EXISTS on that page

how you do this is through your htaccess file. just edit it through your cpanel

here is a link that will explain it

You will have ZERO seo side effects