What does the `required` attribute do in an HTML5 form input element?

The required attribute is a boolean attribute in HTML5. When present, it specifies that an input field must be filled out before the user can submit the form. Here's how it works:

1. First, you have your form element. This is the overall container for your input fields. For example: <form></form>

2. Inside this form element, you have your input elements. These are the fields that users will fill out. For example: <input type="text">

3. If you want to make an input field required, meaning the user cannot submit the form without filling out this field, you add the required attribute to that input element. For example: <input type="text" required>

4. Now, if a user tries to submit the form without filling out this field, the browser will prevent the form from being submitted and display a message to the user indicating that the field must be filled out.

5. Once the user fills out the field, they will be able to submit the form.

So, in summary, the required attribute in an HTML5 form input element is used to make sure that a field is filled out before the form can be submitted.