Although Wordpress is quite intuitive in most cases, there are some things that are not as obvious, such as "Where do you find the the page ID in Wordpress?" This is especially useful if you're trying to exclude by Page ID certain pages that appear in the Pages Widget.
This tutorials will show you how to quickly find the hidden Page ID in Wordpress.
In the left menu click on Pages then the title of the Page.
The Page ID is hidden in the URL. Look for post= and the number to the right of it is your Page ID.