All WordPress themes have a file called page.php. This is your template file for all pages you have on your blog (remember, pages are distinctly different than posts). The page.php
file is your default page template. To create a new one, just open that
file in any text editor then “save as” a different file name. In my
case, I named the template for my sales page signup_page.php.

Now, at the very top of this new file, you’re going to want a block of PHP code as follows:

/*

Template Name: [your page name here]

*/

?>

This is a PHP comment. Leave the “Template Name:” in place, but you
need to change the name of the page. Once you have done that, upload
this new file to your blog theme’s folder.

Then, in WordPress, when you go to add or edit a page, scroll way
down and you’ll see a setting for “Page Template”. You should see your
new page template listed in the dropdown, using the name you entered
above. To the right, you can see what my dropdown list looks like in my
own WordPress admin panel. I have many different custom page templates
in my system, all for different purposes.

How To Use a Custom Page Template In WordPress | David Risley dot com