You can create your URLs by hand or you can use a URL generator. There are three generators. Be sure to use the correct URL generator because the URLs to websites, the Google Play Store, and the Apple App Store are each a little different from each other. the Google Analytics Campaign URL Builder for generating URLs to websites. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.