You need to be at your office or desk phone to forward calls. If that isn't an option try using OSU's Cisco Unified Communication portal (VPN required) or see its instructions.
Remember that voice mails will NOT be forwarded to the destination phone.
Select the "Forward All" option from the phone's menu.
Enter the full phone number starting with 8, just like you would for a phone call. (8 + Area Code + Prefix + Line number)
The phone should complete setup automatically.
Test the forwarding by calling the number.