You define the orientation of your laminate layup with respect to the material orientation specified for the surface. The figures below illustrate the sign convention for the ply orientation relative to the material orientation. The 1' and 2' axes for the material orientation define a right-hand coordinate system with the 3' axis extending out of the plane of the illustration.
For a 0 laminate, the 1 direction of the ply is aligned with the 1' direction of the material. For a 90 laminate, the 1 direction of the ply is aligned with the 2' direction of the laminate.
laminate, the 1 direction of the ply is aligned with the 1' direction of the material. For a 90