Sorry, Spark cannot handle the public-facing website part. We have locked out those Drupal features. Only the CiviCRM features are available.
However, you can use another service to create your website, then point to your CiviCRM forms hosted on Spark (donation form, newsletter signup, event registration, etc).
CiviCRM Spark aims to help people evaluate and get started with CiviCRM. It is also suitable for smaller organisations (larger ones will hit the contact/email limits and will want to customize it more). For those who outgrow Spark or who have more customization requirements, we recommend contacting a CiviCRM hosting partner.