Sometimes themes or plugins might ask you to enter post or page IDs in order to setup some options. Every post and page you create in WordPress has an unique ID number. Here is a simple tutorial to show you how to find post or page ID in your WordPress site.
There are two ways to find out your post or page ID. Navigate to the Pages → All Pages or Posts → All Posts page and hover over the page (post) link. At the bottom of the page you will find a link with an ID number.
Also, you can click on the page (post) link and it will redirect you to the Edit page. Your page (post) ID number will be displayed in the address bar at the top of the page.