Ferry

The word (Required) is just written text. It is possible to type the asterisk manually. However, you can style this also. For instance using CSS:

.required:after{
   content:'*';
  color:#f00;
}

or SASS:

.required {
   &:after{
    content:'*';
    color:#f00;
   }
}

For the guidance, you can for instance put the following in the Contact Form editor:

<p>Please note that fields with an asterisk (<label class="required"></label>) are required fields.</p>

And to use it in the form itself, you could use for instance:

<label class="required">Your Name</label> for required field labels and <label class="anything_but_required">Your Name</label> for the optional fields.

This makes it consistent throughout.