URL shortening is a way to make a URL substantially shorter and still direct to the required page.
www.google.com will look like this when shortened by using bit.ly:
Suppose www.evilcyberhacker.com is a malicious site, which is shortened to:
There’s no way to distinguish by observing these two shortened links that one of them is malicious. If you click the malicious link you could be in all kinds of trouble.
So what can you do?
If you want to retrieve the original URL from a shortened link before clicking on it and visiting the destination you can simply add a ‘+’ behind the shortened URL.
If the URL looks suspicious you can then scan it with tools like Virustotal.
Another option is to use tools like https://checkshorturl.com/ which expand the shortened link and provide the option to check the original URL with several online scanners.