How do I create a custom form in the account area?

To create a form you need to create a class that extends the 
\Aero\AccountArea\AccountAreaForm class:
The 
$sections array lists the views used to render the form.
The 
method() method defines the method that the form will use (this should be 
post, 
get, 
put, or 
delete).
The 
route() method should return the URL for the form.
 A 
$data variable is accessible in case the route requires parameters that are available in the data.
For example, here's how the login form is defined:
class LoginForm extends \Aero\AccountArea\AccountAreaForm
{
    protected $sections = [
        'email' => 'account-area::partials.email-input',
        'password' => 'account-area::partials.password-input',
        'forgot-password' => 'account-area::partials.login-forgot-password-link',
        'submit' => 'account-area::partials.login-button',
    ];
    protected function method(): string
    {
        return 'post';
    }
    protected function route($data): string
    {
        return route('login');
    }
}
Don't forget to register your form:
\Aero\AccountArea\AccountArea::registerForm(MyForm::class);