To add a forwarding address to Google Apps account follow the steps below
1) Login to your email id
2) Click the gear in the top right
3) Then click on Forwarding and POP/IMAP tab
4) In forwarding section click the "Add a forwarding address
5) Enter the email address to which you'd like your messages forwarded.
6) For security, Google Apps send a verification to that email address
7) Open your forwarding email account, and find the confirmation message from the Gmail team
8) Click the verification link in that email.
9) Back in your Gmail account, select the 'Forward a copy of incoming mail to...' option and select your forwarding address from the drop-down menu.
10) Select the action you'd like your messages to take from the drop-down menu. You can choose to keep Gmail's copy of the message in your inbox, or you can send it automatically to All Mail or Trash.
11) Click Save Changes.