Most fabrics have designated sides that are meant to be “seen” and “not seen”. Each side will likely have a different color or texture, or both. If your fabric has a design printed onto it, you will notice that the “right” side is more vibrant.
To sew the two pieces with RIGHT sides together, place the sides of the fabric that you want to be seen (the printed/smooth/preferred sides), and then sew as instructed. When the fabric is turned right side out, the seam will be hidden.
To place the WRONG sides of the fabric together, place the unwanted sides together, and sew as instructed.