Option Description
ReCaptcha Public Key ReCaptcha is used to prevent spam in contact form page.
if you enabled the contact form then you must have ReCaptcha Public Key and Private Key.
Learn How to Get ReCaptcha Public and Private Keys.
ReCaptcha Private Key the same as ReCaptcha Public Key
YouTube API Key You must have YouTube API Key to import videos from youtube.com
Learn How to Get YouTube API Key
Facebook Admin ID it is used for facebook graph protocol (when you moderate facebook comments)
Twitter Account Username it is used for twitter meta data
Google Analytics Tracking Number to allow google analytics track your site you must add the Google Analytics Tracking Number
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');

ga('create', 'UA-74704459-1', 'auto');
ga('send', 'pageview');
We only need this bold one : UA-74704459-1