Field help (STG2LIBCAT) 

To select several values, click the Actions icon, and then click Multiple values: you can enter a criterion or a range of criteria, or both.

The Category, Company, Site, Target job type, Position, Population and Authorization fields are multiple-valued fields. The field becomes green when it contains a multiple selection. If the field does not have a multiple value, you can click the Selection icon. Otherwise, modify the selection by clicking Multiple values.