When I am going to set alert, it says Operator is required. How to overcome this problem? Plz answer

When I am going to set alert, it says Operator is required. What should I do?

You need to specify when alert should be triggered, without operator alert won’t be set.

Look at this example

Thanks for reply. What is meaning of " Without operator" kindly eloborate. What is operator?

Look at the area highlighted in red, these are the operators.

You have to tell the system when you want alert to be triggered, and these operators make it possible. If you don’t specify when an alert should be triggered then the alert won’t be created.