Anything related to the Web Forms For Marketers module.

Web Forms for Marketers (WFFM) is Sitecore's free module that allows marketers to create and publish simple forms, usually without a developer's help. It provides an easy wizard interface to define form fields with pre-set types, validation rules and save actions that determine what happens on form submission.

https://doc.sitecore.net/web_forms_for_marketers

https://doc.sitecore.net/web_forms_for_marketers/82/setting_up_web_forms

https://www.youtube.com/watch?v=P4uyxf1FNtY

http://www.nonlinearcreations.com/Digital/how-we-think/articles/2014/10/Sitecore-Web-Forms-Marketers-Tips.aspx