This functionality activates when it finds multiple form tags in the HTML for a page, e.g.

<form id="form-1">

<fieldset></fieldset>

<input type="submit" value="Submit Form 1" />

</form>

<form id="form-2">

<fieldset></fieldset>

<input type="submit" value="Submit Form 2" />

</form>

There's nothing special that you need to do.