The subscriber confirmation email settings are automatics.
In the List tab, click on the option button of the list, then on Subscription form.
You can customize the form in the window below:
On the left area, you can move the blocs by clicking on 
or delete them by clicking on 
which displays on rollover.
You can add Text area, Title, Image by drag and drop from the right menu.
You can add custom fields and customise your form with the options under the Design tab.
Click on Options to copy the HTML code or view the form online.