What is Facebook ID and way to find it by manual?

Facebook UID is a unique number assigned to your profile.

Some social plugins and social apps need Facebook personal ID and Facebook page ID
For integrations of certain Facebook social plugins, like the "Like" button and "Like box", and others,

To find your UID on Facebook:

1. Log in to your Facebook account.
2. At the top of the Facebook page, there is a navigation bar in the upper right corner with options like Home, Profile, and Account. Click Profile.
3. At the top of your browser, you will see a URL that looks like this

If you have the vanity URL you can find your Facebook ID by following these steps:

1. Go to your timeline.
2. Move your mouse pointer onto your current Profile Picture.
3. If your browser has a status bar enabled at the bottom of the screen, it will show an URL.
4. The number behind the dots is your id. For the example below "123456789" is the ID.
5. https://www.facebook.com/media/set/?set=a.111051224565362.24509.123456789&type=1
6. If you don't have the status bar you can copy the shortcut by right-clicking and paste into a text document.

If you have trouble finding your Facebook UID:

Just use this tool "Find FB UID" to find your Facebook UID in an easy way.

Reference from (uib.com)