A rolled hem is a lovely neat way of hemming fine fabrics like silk. Run a line of basting along where you want the rolled hem line to be. Allowing 1/2″ from the edge of the fabric gives you more fabric to work with for the rolled hem. Allowing 1/4″ gives you a smaller roll. I usually use somewhere between the two. Add a line of machine stitching half way between the basting and the edge of the fabric.
Working on the wrong side of the fabric, roll the edge of the fabric down to the line of basting which is marking where you want the hem to be. This actually sounds easier to do than it is! The way that works for me is to fold over a small allowance and then fold over again to bury the raw edge. Gently push the fold back up to the line of basting for the rolled hem.
Slipstitch in place along the line of basting. There isn’t room to pin so you have to keep adjusting the hem as you sew. When you have finished, remove the basting. Sewing a rolled hem is fiddly but well worth it if you are making a silk scarf, for example.