You can easily add a form to your site by creating the form with a third-party form builder, then embedding it on your page via the embed element. Brandcast does not yet support the creation of custom forms within the Design Studio.
For more detailed information about how the embed element works, refer to this article.
Some form builders will give you the option to capture payments from your users (via PayPal, Stripe, Square, etc.), allowing you to create simple order forms without the need of a shopping cart.
Below is a list of some third-party form builders that you might consider using. Each of these tools will provide you with embed code that you can use to render the form in your Brandcast website.