A properly set table has the napkin placed to the left of the dinner plate. Whether it is folded into a triangle, square or rectangle, the napkin is placed with the folded edge to the left and the open edge to the right.
During the Middle Ages people used their hands to eat and the only place to wipe their hands was on the edge of the tablecloth. Changing the tablecloth frequently was a necessity. The French started adding an extra cover to the table's edge which made it easy to change while not disturbing the guests or settings. This cover eventually was detached to allow guests to wipe their lips; this lead to individual linen napkins.
When setting a table, the napkin can either be neatly folded or rolled and inserted into a napkin ring, and then placed to the left of the dinner plate. It can also be attractively placed inside a wine glass or placed in the center of the dinner plate.
In the late 1700s the standard napkin size was 45 by 35 inches. By the 1800s, cloth napkins were commonly used and, to add interest to the place settings, hosts came up with a variety of creative ways to fold the napkin.