On a Smart Site you can edit the standard contact form field labels.
On a Pro Site you can also add new fields, including Multiple choice fields, check-boxes and more.
Simply go to the Contact page, click on the Contact form, and you will be able to edit the field labels and add new fields.
On a Pro Site you can also add a contact form block to any regular page and customize it.
Watch the tutorial video:
How To Create A Form