When you're a beginner, zippers are something to be avoided and a separating  zipper sounds even scarier.  A separating zipper is different than a regular zipper because the two sides of the zipper become totally separated when unzipped.  This difference means that sewing one in, can also be a bit different.   Don't be scared because you can totally sew in a separating zipper with very little stress.  Not only that but, it'll make your outerwear garments look professional with this extra feature and no will guess that your garment is homemade!