The name the element has in the form goes inside the brackets.
So if your form has
<input name="name" type="text" id="name" tabindex="16" />
After the form is submitted, PHP can assign the value posted to the variable. Here we assign the value of the textbox above to the variable $nameField:
$nameField=$_POST['name'];
Now if you want to use that variable in your email, you'll need to use the variable just defined.
$body = <<<EOD
<br><hr><br>
name: $nameField <br>
Get it??
Lost time is never found again.
- Benjamin Franklin