If the picture on the screen is landscape.
And you put the paper/card in in Portrait, then you tell the printer to print Landscape.
If the picture on the screen is portrait.
And you put the paper/card in in Portrait, then you tell the printer to print Portrait.
This can/could get very confusing, so basically, if one setting prints incorrectly, put the paper/card in in the opposite way. (Without altering any of the printer settings)
Personally with envelopes I always insert them in landscape, that way the roller/s have a wider area to grip with, plus the print-head has less passes to travel.