FAX ONLY mode is best used when you have your FAX/MFC on a dedicated fax line. In this answer mode, the FAX/MFC automatically answers every call with receiving tones as if it were an incoming fax. If you select Fax Only mode, you cannot receive incoming voice calls on the telephone line your FAX/MFC is connected to, though you can make outgoing calls on the line.

In MANUAL mode, you control the telephone line and must answer every call yourself. If you answer the line and hear fax tones, wait until your FAX/MFC begins to respond with its own receiving tones, then hang up the phone. The FAX/MFC will receive the fax and print it out. You can receive incoming voice calls when using this answer mode just as you would if the FAX/MFC was not present on the line. This mode is preferable if you do not receive many faxes, if the FAX/MFC will be on the same telephone line as a computer modem, or if you are using Distinctive Ring.

FAX/TEL mode is optimal if you receive lots of faxes and few telephone calls. In this answer mode, the FAX/MFC will automatically receive and print incoming faxes. If you receive a voice call, every phone on the same line as the FAX/MFC will ring a designated number of times, after which the FAX/MFC will begin to double-ring to notify you that the incoming call is a voice call.

TAD:MSG MGR or MC:MSG CTR mode is to be used when you record incoming vioce messages and automatically receives faxes. In this answer mode, the FAX/MFC automatically answers every call. Voice messages are stored on the FAX/MFC while fax messages are printed or stored on the FAX/MFC.
When using the this mode, these guidelines MUST be followed:

1. Your answering machines outgoing message must be no more than 20 seconds long.
2. You must end your outgoing message by giving your Fax Receive Code for people sending manual faxes.  For example: "After the bleep, leave a message or send a fax by pressing *51 and Start, Fax Start or Start/Copy