Answer:
It is not necessary to use a different coordinate system to specify the loads. The loads can be applied in the local z-direction if they are to act rectangular to the surface.
Please note the projection plane when specifying the loads. From the point entered in the Load Position section, a straight line is "constructed" perpendicular to the load projection plane. If this line intersects with a surface contained in the "On Surfaces No." list, the load is then applied at the point of intersection. This way, you can easily apply similar loads on many surfaces.
The boundaries of the surface load are where the gray dotted lines intersect with the surface. The surface load is also displayed in this way when it acts perpendicular to the surface.
For the graphical specification of the coordinates, a local coordinate system may be useful, of course.
