"Materials" button displays a tree of materials consisting of three tabs. The tab "General" is common for each material.
The next two tabs contain several tables. Number of columns can be changed in these tables: the columns could be shown or hidden.
Example:
If "Concrete" is selected from materials tree, three tabs in the right part of the window appear (General, Analysis, Concrete):
In the "Analysis" tab you can see the table with 5 columns: "Description", "Density", "Elasticity", "Poisson" and "Linear Expansion". Some columns can be hidden using 
"Material Grid Designer" button. After clicking this button the "Material Types Grid Designer" window will be opened. Select "Concrete" from "Select material type" drop-down list:
Concrete tabs are shown in the left part of the window. After selecting "Analysis" tab the table (with two columns: "Select" and "Column name") appears in the right part of the window. The columns are shown if check marks are on, otherwise columns are hidden.