Glide reflection is a composite transformation which is a translation followed by a reflection in line parallel to the direction of translation. The order of the two constituent transforms (translation and reflection) is not important. One can easily verify that the same result is obtained by first reflecting and then translating the image.
Unless the translation part of a glide reflection it trivial (defined by a 0 vector), the glide reflection has neither fixed points, nor fixed lines, save the axis of reflection itself. If the translation part is trivial, the glide reflection becomes a common reflection and inherits all its properties.
All these properties are implied by the definition of the glide reflection being a product of reflection and translation. The importance of the glide reflection lies in the fact that it is one of the four isometries of the plane.