In shell pattern two dots are connected with pulled stitches which are knotted and separated by a slack knotted stitch.
Mark squares of 2 .5 cm x 2.5 cm on the wrong side of the fabric. Mark the red diagonal lines that represents pulled stitch. Mark the numbers 1,2,3,4,....while learning, as it will be easier to follow the diagram.
.Stitch with 3 strands of Anchor thread of the colour that matches the fabric. Folds look good if satin material is used.Follow the steps and stitch all the rows.2 rows of the squares are used at a time. I have explained them with images. please see below.