Solution:

1) If the Database window is not active, activate the Database window.
2) Open the table's Design view.
3) Do one of the following to add a field to the table:

a) To add the field to the end of the table, click in the first blank row.
b) To insert a field within the table:

1] Click in the row above which the field is to be added.
2] Select the 'Insert' menu and select 'Field'. (The row appears above the selected row.)

4) Type a name for the field in the 'Field Name' column.
5) Click in the 'Data Type' column. (A down arrow appear.)
6) Click on the arrow in the 'Data Type' column. (A drop-down list appears.)
7) Select 'Yes/No' from the 'Data Type' drop-down list.
Yes/No
NOTE: If 'Yes/No' is not on the list, select either 'True/False' or 'On/Off'.
8) To set a format for the field:

a) Move to the 'Field Properties' section.
Field Properties section
b) Click the 'General' tab.
c) Click in the 'Format' property box. (A down arrow appears.)
d) Click on the arrow in the 'Format' property box. (A drop-down list appears.)
e) Select 'On/Off' from the 'Format' drop-down list.

9) (Optional) Set other field properties for the added field:
Field Properties section

a) Make any other desired entries and selections for the 'General' tab.
b) Click the 'Lookup' tab.
c) Click in the 'Display Control' field. (A down arrow appears.)
d) Click on the arrow in the 'Display Control' field'. (A drop-down list appears.)
e) Select the desired control for the 'On/Off' field from the drop-down list.
NOTE: The choices are 'Check Box', 'Text Box', and 'Combo Box'.
f) (Special Case) If 'Combo Box' is selected in step 9)e), make the desired entries and selections in the additional properties that appear for the 'Lookup' tab.

10) Select the 'File' menu and select 'Save'.
11) Select the 'File' menu and select 'Close' when finished making changes in the Table Design window.