The OrderBy property is a string expression that is the name of the field or fields on which you want to sort records. When you use more than one field name, separate the names with a comma (,).
When you set the OrderBy property by entering one or more field names, the records are sorted in ascending order.
If you want to sort records in descending order, type DESC at the end of the string expression.
For example, to sort customer records in descending order by contact name, set the OrderBy property to "ContactName DESC".
I got this straight from Microsoft Access Help. It explains it better than I could.