German Short Rows / Shoulder and Neck Shaping 

This video demonstrates how to work German Short Rows to shape the shoulder and neckline.
Instructions will say to purl until x number of stitches remain on your left needle, TURN, GSR.
The GSR / Double Stitch is created as follows:
With working yarn in front, slip the next stitch from your left needle purlwise to your right needle, pull the working yarn over the right needle to create a double stitch, (you should see 2 legs on the double stitch) keep the tension on your working yarn and proceed to work starting with either a knit or purl stitch as indicated on your pattern.
Note: When working a purl row following the GSR/ DS you will bring your yarn to the front of your work and then begin purling.
When working a knit row following the GSR /DS your yarn should remain behind your work and you can begin knitting as usual.
To resolve a DS, you will work the 2 legs of the Double Stitch as 1 stitch. Similar to a K2TOG, or P2TOG.
When decreasing to shape the neckline, you will work K1, SSK, or a K2TOG, K1, depending on whether you are working the left or right side of the neck shaping.