First things first - what is a vanity URL?
For example, RunRedDeer.com organizes a race series of 3 separate races, one of which is the Halloween Half Marathon. On the event poster, they could display
Yup, vanity URLs are cool.. How do I get one? How do I set it up?
I'd suggest buying your new domain from your existing domain host just to keep all your domains easy to track in one account, but you can buy it from any domain provider.
2. Create a trackable URL
Now that you own the domain, you'll want to update the DNS to redirect the domain to a specific page on your website, BUT if you want to actually know how many visitors use your vanity URL, you first need a URL that Google can track.
Log into your domain manager and use the "forward" or "redirect" option to paste in the URL you generated. Test your vanity URL to confirm it redirects correctly (with the tracking data).
4. Track Vanity URLs in Google Analytics
Log into GA and select the property you set up the vanity URL for.
Under Acquisitions, click All campaigns.