Regular expressions is Google Apps method of forwarding emails for selected users (rather than all Google App users).
To select the users use the first part of their email address (before the @ symbol) in a regular expression.
Here is an example of a regular expression for "mydomain.com." Of course yours will substitue your users' names followed by your doman name in the same manner.
Note there are no spaces between the vertical slash symbol ( | ) or between the parentheses separating the names from the @ symbol and your domain name.
In the same area you added your forwarding address add your own regular expression to option 3. under 'Execute this setting only if the envelope sender matches' as illustrated in the picture below.
Make sure the Execute box is checked. Click save!