1) Visualforce allows users to build customized user interfaces for Salesforce using an MVC framework and Visualforce markup tags. 2) Visualforce pages can be used to create internal and public facing pages, dashboards, and customized components. 3) In Salesforce 1, Visualforce pages can appear in the navigation menu, as publisher actions, or on record home pages as mobile cards. Certain considerations need to be made to optimize Visualforce pages for the mobile environment.