Firstly, provide a Title for your form and select the Theme, which you would like to use for its display. If you wish to have it displayed with the styles of your website theme, choose Inherit From Website Theme option from this drop-down.
Press on the arrow from the right side to open form header settings. Here you can set a Title which will be displayed above your form. Additionally, the MailChimp WordPress plugin lets you write a few lines of Description for your subscription form.
If you wish to have a picture on your form header, click on Upload Image button. WordPress Media Library popup will open for you to select or upload one. Furthermore, you can set Animation on it, such as Bounce, Pulse, Flash and more. You can also set to hide this image on mobile browsers with the corresponding option.