Autofill is meant to stay out of your way ("set and forget"), that's why you don't see any toolbar buttons or icons for it.
Everything is accessible through the
right-click context menu.
The easiest way to
get started is to let the built-in wizard create the autofill rules
for you.
To summon the wizard, simply
right-click on any page with a form and
select
Autofill / Add Rules for this Form... from the context menu.
The wizard should appear; just follow the instructions and the
autofill rules should be created for you automatically. The next time
you load that page, the form should be autofilled with the data you
defined. If you want to create an autofill rule for one particular
form field only, then right-click inside that field and select
Autofill / Add Rule for this Field.
Here are some video tutorials to show you how to create your very
first autofill rules:
Adding rules using the wizard...
http://www.youtube.com/watch?v=0_50PjfRqUE
Adding rules manually...
http://www.youtube.com/watch?v=laabxmw4Avk