Mathematica's unique structure allows a generalized notion of input, in which not only ordinary text, but also typeset structures, diagrams, graphics, control objects and even complete user interfaces can be entered and immediately return values that have been associated with them.
DynamicSetting — display as a control that dynamically gives its setting when evaluated
Ctrl+Shift+Enter — evaluate in place to show the displayed form
Manipulate — set up a collection of controls
Interpretation — specify any interpretation for a graphic or other expression
