Update 3 2 open data

3-2-open-data.md

@@ -13,6 +13,7 @@ To open a file or a directory containing multiple files:
 
 ### 2. Using *Variables Pane* to manage variables.
 
+**Variables Pane** consists of two components: control bar and display area.
 After opening data files, the **Variables Pane** displays a hierarchical tree structure (*File Name* -> *Category Name* or *Vertical Coordinate System* -> *Variable Name*) of the variables in your data. 
 
 ![](img/3-2-2-variables-pane.png)