It is sometimes necessary to obtain the ID of a Post or a Page so that specific Pages/Posts can be excluded/included in Block settings.
Here are two ways in which you can determine the ID of a Page or a Post in WordPress:
Go to the list of all Pages in the WordPress admin at Pages > All Pages.
Place your mouse on top of the Page whose ID you would like to get and take a look at the URL in the status bar.
The number that appears after
post= is the ID of that Page.
The same process applies for Posts (or entries of any other post type) as well.
Use a plugin like Show IDs by 99 Robots which adds a admin column showing the IDs.