The process is exactly the same as if you were purchasing an item: click on ‘continue to payment’ and follow the usual steps. Obviously you will not be asked to provide payment details in the end, and therefore you will not be charged for anything.
This pattern is designed to use a single 100g skein of fingering weight yarn. The shawl is just wide enough to go around the shoulders, and can be fastened with a shawl pin to keep the garment in place without too much of a stretch.
The shawl in the photos measures 82 cm / 32” across top edge, and 38 cm / 15” in height at midpoint.
For a wider shawl, increase the number of stitches at cast on by multiples of 16 sts, none of the subsequent instructions will need to be altered. Casting on 314 sts would give a mid-sized shawl, and will use up approximately one and half 100g skeins of fingering weight yarn.