Details on the Formation of Forms

Forms are useful tools for your website.  Here are a few ways to use them.

For simple forms: https://drupal.org/project/webform.  You can try it out in more detail here: http://webform.com

For forms that need to use the flexibility of drupal fields, rules, etc: https://drupal.org/project/entityform.  These are more complex to setup, but very powerful.

For multiple choice, long answer, etc quizzes: https://drupal.org/project/quiz.  This is limited in its expandability and only really helpful for quizzes.

For things that don't need to be embedded in a site, and that you'd like to tie to google docs, you can use: http://www.google.com/google-d-s/createforms.html

If you're doing things far more complex than that you may want to look at external services like: https://www.surveymonkey.com  

If none of these fit the bill then you can build something custom in drupal, you just need to know the form api:

Form Generation: https://drupal.org/node/1702548
Form submission: https://api.drupal.org/api/drupal/includes!form.inc/group/form_api/7
 

Altering forms: https://drupal.org/node/1702628
Form API Reference: https://api.drupal.org/api/drupal/developer%21topics%21forms_api_reference.html/7

You can then tie your webform or custom forms to outside services if you'd like using the following:

https://drupal.org/project/salesforce
https://drupal.org/project/exact_target_api
https://drupal.org/project/mailchimp
https://drupal.org/project/sfweb2lead_webform
https://drupal.org/project/constant_contact
https://drupal.org/project/simplenews