How can I put my own code in a wordpress page?
you can make wordpress single page template and put your own code and assign this template to your page wordpress templates
You can do this by using the native page templates feature in Wordpress.
Simply create a new file under your parent/child theme. ex. my-template.php. This file has to start with a PHP comment that defines the template name like this:
<?php /* Template Name: My Cool Template */ echo "My custom page template!";
After you save and upload the file, you'll find the template in editing page under Page Attributes box:
Note that in most cases you just want to add or modify something in the main template and don't want to lose the whole design. In this case I recommend you copy the code of page.php file in your theme to the new template file you created, and just add you modifications to it. If page.php doesn't exist, just use index.php instead.