Once the first stitch is completed, now pick up the working yarn and complete the next stitch. In doing so the working yarn passes over the "tail" and anchors it so that the first stitch doesn't slip. When the garment is done, work the "tail" into the knitting as you would normally do.
Step 2 of adding new yarn
I am so glad that I learned this trick for adding yarn at the end of the row. It makes it so much easier to do.