Check out example codes for "kak ispolzovat html checkbox". It will help you in understanding the concepts better.

Code Example 1

<input type="checkbox" onclick="checkFluency()"  id="fluency" checked />

Code Example 2

function checkFluency()
{
  var checkbox=document.getElementById('fluency');
  if(checkbox.checked!=true)
  {
    alert("you need to be fluent in English to apply for the job");
  }
}

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