Itai,
You will need the HTML markup. It'll look something like this:
<form action='http://example.com/form.php' method='post'>
<input type='text' name='name' value='Name here' />
<input type='submit' value='Go' />
</form>
Once you've got that, open your landing page (click "Edit Draft") and simply copy and paste the form markup into the page where you want it to appear.