Microsoft Access Field Properties – Required

Required 

Field properties are where you fine tune the table.  The data type provides general information about the type of data that a field is going to contain and in the properties is where you define it more exactly.

When this property is set to Yes, you must enter a value in the field to save the record.
When a form is set up to add new data, this field must be included on the form or it must have a default value set up otherwise the form will not allow you to save the data.

If the data might need to be entered later then do not set the required property to yes.
In a text field if allow zero length is set to yes then the field will accept  “” . It will appear as if there is nothing in the field.  If you wish to prevent this from happening then set the Allow Zero length to No.