The Material Substitution Entry window is where you find the options to configure material substitutions for Summary.
Active: Check this option to make this material substitution active for the Summary Report.
Single Key: Use this option to set up a material substitution for only one Key. When using this option, the From Key(s) field is a drop-down list and To Key: field becomes active.
Selected Keys: This option allows you to apply a material substitution to multiple Keys. When using this option, the From Key(s) field becomes a list of available Keys while the To Key: field becomes inactive. Select any Keys you wish to use the material substitution from the From Key(s) field.
From/To Category/Keys: These fields allow you to select which Categories and Keys you wish to substitute.