If you're a Professional, Premier, or Enterprise user, you'll find the Branding feature in the General Settings page. Click the Define a header and footer for your forms link to open the Branding Editor:
Once there, you'll see three check boxes: Page Header, Page Footer, and HTML <HEAD>.
By default, all boxes will be checked and the default header is blank. If you want to add a custom header and/or footer, uncheck the box of the section you would like to customize.
A text area will appear, where you can add your company's logo, navigation options, links, legal terms and conditions, or contact information. You can style these as much as you like, and copy existing HTML to ensure that your forms fit seamlessly within the rest of your website.
The header, footer, and <HEAD> section will be applied to all your forms, so you only have to set it up once.