Form elements are not obvious always with their labels. Certain situations users need additional information in the form of instructions. While paying bills using a credit card, the form ask for CVV. For first time users, they may not know what is CVV, and where is that available. So an additional instruction ‘CVV is a 3 digit number available at the back of your credit card’ is an instruction provided for the user.
<label>CVV</label>
<span> CVV is a 3 digit number available at the back of your credit card’</span>
<input type=‘number’ id=‘cvv’ />
Format of dates, new password instructions, identifying mandatory fields etc are some situations where additional instructions are required for a form field.