If the command selected in the Command field takes a parameter,
you can determine the parameter here.
If the command has a relation to another table (such as the Item table), you can use the lookup button to select from that table.
If the command takes a parameter that is predefined in the POS Parameter Setup for the command, you can see the parameter options by clicking the AssistButton to the right of the field.
Commands such as BOMMENTYPE, MTYPE_CHG and POPUPMENUTYPE have both lookup options.
Parameters for each command are described here: Commands and Hospitality POS Commands.