Today we will talk Form API. The API allows to expand your Drupal installation with highly extendable and secure forms. In this particular post I will show how to create a multi-step survey with file upload ability. Form API is part of Drupal's core and there's no need to download it.
To make it easier to implement multi-step forms we'll use Chaos tool suite, an additional set of API's made to further streamline developing.
All code will reside in a custom module. For the purpose of this tutorial let's call it multi_step_form.