Printing envelopes involves two stages. You have to create the envelope page format in whatever word processing software you are using, e.g. Word. Once you have got the document ready and saved (always save before you print!), then you must ensure that the printer is recognized by your operating system and has the full device drivers installed.
Your printer manual has the correct setup for how to configure the printer, but essentially all you have to do is put the envelope in the correct tray, ensuring that the envelope is correctly aligned and the right way up and then print the file from your word processor.
cheers, TREVOR
Before you ask us, have you looked in the manual or on the Canon Support Site?
"All the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
