Support teams, software engineers, and developers deal with hundreds, if not thousands, of reports of bugs, issues, troubles, you name it. Actionable Issues clearly describe what the issue is, how it affects you, where the issue occurs, and how to reproduce the error (if applicable).
Let's look at a fictional example of a user reporting that they are having issues logging in to a website.
Bad
"I cannot log in"
While it is unfortunate that the user cannot log in, they provided no information! They could be having trouble entering their password, forgot their password, getting an error at log in, entering the incorrect email/username, their connection might be spotty, it could be anything! This is not actionable because we cannot do anything without probing the user for more information, which can often feel like pulling teeth for us.