Adjust the edge guides to match the width of the paper that you are loading.
Load a sheet of paper with the printable side facedown.
Load letterhead with the printable side facedown and the top edge entering the printer first for one-sided printing.
Load letterhead with the printable side faceup and the top edge entering the printer last for two-sided printing.
Load envelope with the flap side up and against the right side of the paper guide.
Feed the paper until its leading edge gets pulled in.