When you search for something on google it takes you to a results page. Here, google shows you all the relevant pages for your search query. If you click on any of the results, google takes you to the actual website or webpage. However, the HTML link that you click on takes you to a google's page first and from there redirects you to the target web page. This is done for various purposes such as tracking. Use this tool to grab the actual URL of the webpage without actually clicking on the Google redirect URL. Perhaps you just want to grab the URL and bookmark it somewhere or put it on excel. This method also prevents you from visiting the webpage of the search result.
Google URL shortener is used to create redirect links which are very short in size and can be shared in various social media and chat platforms. On clicking this link, the user is redirected to the actual web page which most likely has a long and winding URL difficult to share in such platforms.