Are you an administrator of the system? These are pretty trivial, yet assume some knowledge of the system, so perhaps you may want to hire a professional? However if you feel you can handle it, the high level steps are:
1. Configure the voice gateway with MGCP protocol
2. Build the Gateway in Communications Manager, define the port to point to internal extension via attendant field
3. Build a phone with that extension
Keep in mind an FXO port does not deliver DIDs, it is simply one number, just like a traditional home phone line.
HTH,
Chris