You can use the TDBLookupComboBox (you shuold have it in the DATA CONTROLS).
Hereafter a snippet of the help of this control.
<i>TDBLookupComboBox represents a combo box that identifies a set of field values in one dataset with a corresponding set of values from another dataset.
Use TDBLookupComboBox to provide the user with a convenient drop-down list of lookup items for filling in fields that require data from another dataset.
If TDBLookupComboBox is linked to a lookup field component, it automatically reads the relationship between the field value and the lookup values in the lookup dataset from the field component. The relationship between field values and the corresponding values in the lookup dataset can also be explicitly set using the properties of the lookup combo box when the combo box is not linked to a lookup field component.</i>