Here you add the xml code. Use Joomla! xml style for form. Params U see here. As textarea doesn't allow , use [ and ] instead. So the form xml might look like that.

[form]
[fieldset name="fieldset1"]
[field name="name" type="text"  size="50"
required="true" /]
[field name="email" type="email" size="50"
required="true" /]
[field name="subject" type="text" size="50" /]
[field name="message" type="textarea"
cols="50" rows="20" required="true" /]
[/fieldset]
[/form]

You must use a form tag and a fieldset tag. Fieldset tag MUST have a name, otherwise Joomla! can't display fields

You can add additional fieldsets with (or without) labels, e. g.

[form]
   [fieldset name="fieldset1" label="Personal data"]
     [field name="firstname" type="text"  size="50"
     required="true" /]
     [field name="lastname" type="email" size="50"
     required="true" /]
     [field name="subject" type="text" size="50" /]
     [field name="message" type="textarea"
     cols="50" rows="20" required="true" /
  [/fieldset]
  [fieldset name="fieldset2" label="Adress data"]
     [field name="street" type="text"  size="50"
     required="true" /]
      [field name="suburb" type="text" size="50"
      required="true" /]
      [field name="zip" type="text" size="50" /]
  [/fieldset]
[/form]

In case you get the error message "invalid form" while saving. This refers not (!) to the xml in the textarea field. Just add a valid e-mail address in the e-mail address field.

By the way, this is why the param section "e-mail settings" is marked with an asterisk (*).