Start by cutting squares out of your fabric. For 11.5 inch finished napkins, I started with a 14 inch square.
Then iron your sides to sew. Begin by ironing a 1/4 inch down on each side.
Then tuck your corners in.
Including the tucked in corner, iron all sides down 1/2 inch.
Pin your corners.
Sew down your ironed edges. Stitch as close to the edge as you can.
There you are, a nice stack of dinner napkins for your next party.