Plug in the RJ-11 cable at the phone jack and the MX340. Press the Fax button and then the Menu button to get the Fax Settings menu. Press the left/right arrows to highlight Fax Receive Mode. Then press OK. Select Telephone Priority Mode (you will always pick up the handset and then put it down if the call is a fax. If an answering machine is connected the Fax will be automatically answered), Fax Priority Mode (the fax will be automatically received. If you hear the machine's ringtone, pick up the handset and press Stop to answer the call.), Fax only or DRPD (distinctive ring - available extra from your telephone company). Press OK to save the setting. If you choose DRPD, you will need to teach the distinctive ring by calling the MX340 after setting the machine to listen to the ring. (See the manual.) To fax out, press Fax, put your item to fax face up in the ADF and then dial the fax number of your receipient.
Canon has the manuals for the Pixma MX340 available here: http://usa.canon.com/cusa/consumer/products/printers_multifunction/office_all_in_one_inkjet_printers/pixma_mx340?selectedName=BrochuresAndManuals#BrochuresAndManuals
I hope this helps.