Colleague above wrote everything correctly, just in case, try this information submitted is deployed.
1. Safety. Before you start editing -- make a full backup, for example, using the WP All in One Migration, in order to fully recover.
2. If your site is working based on existing themes — makes sense before finalizing / making changes (creating a page with a separate template is exactly what it is) to create a child theme. This will allow a) to divide your revision and what was done b) when you update the theme the changes will not disappear) you can always disable the child theme, if something broke
Plugin to create child themes: https://wordpress.org/plugins/orbisius-child-theme...
3. Once you have created a child theme. You need to create a new template file. For example page-main.php (the name of the file, in General, does not matter). And the main thing in this file in the first line to write . In this case, the file is interpreted as a page template in the edit interface page you have the option to choose this template
4-A. If your design never beats the main design of the website, in the file page-main.php after the first line just paste the whole layout.
4-B. If the cap and the basement are the same as on the website, then your file will look like this
<?php //Template name: the Name of your template ?>
<?php get_header(); ?>
Here can go any your layout
<?php get_footer(); ?>
For proper installation of your scripts and styles -- copy them to the folder with the theme and connect them, writing to the file functions.php your child theme as described above Eugene
5. Create a page in WordPress interface and pick the template you just created. Let's see if the result is correct-designate the home page