Purchase the zipper that is closest to the color of your fabric. If there is a selection that is close to the fabric, utilize the closest color that is slightly darker in color. Zippers are purchase in length size, and type. There are invisible zippers, metal zippers, nylon zippers in several lengths. The back of the pattern will give the length of the zipper needed, so utilize this information.
There are two different kinds of zipper application (Lapped zipper or Centered zipper)
Typically the lapped zippers are for skirts and pants. The centered zipper is mostly utilized for dresses, skirts and pants.
The zipper instructions are given inside of the zipper packages purchased. These are some general instuctions, but it will be important to follow your pattern and zipper installation procedures on the zipper package.
You start with the seam basted closed on the fabric. Then lay the zipper in the position face down on the garmet unzipped. Baste around the first side of the zipper, Zip up the zipper and baste up the other side of the zipper. Once you know it is in the right positioning. Stitch.