They want you to attach the topcase mounting system first. Then the sidecase brackets mount to the topcase mounts and passenger footpeg mounts.
On the topcase mounts, GIVI suggests taking off the grabrail and whatever else would prevent you from sliding the bodywork back far enough to let you get at the bolt on each side that each exhaust hangs from. You are supposed to remove each of those stock bolts and, while supporting the exhaust cannister, insert a longer bolt supplied by GIVI that passes through the hole in the exhaust bracket and the hole in the bracket at the forward end of the topcase mount.
I found it was easier to do this on each side prior to connecting the case mounting plate (big black plastic plate). This also makes it easier to slide the bodywork back forward . You might find it seems as though the topcase mounting "rails" on each side are preventing you from sliding the bodywork back forward, but if you orient them correctly, you will find that it can be done w/o forcing anything. Something to watch for at this stage is proper positioning of the seat lock mechanism "finger"...because if you don't re-position it correctly, everything will appear to be in place, but the latch won't function.
Then reattach the grabrail using the GIVI-supplied bolts and sleeves. I would keep these seated and only loosely tightened until you attach the black plastic mounting plate. Then tighten everything up. Once in place and tightened, this unit is very strong.
This is from memory....but will easily get you in the right neighborhood. My instructions assume you have all the hardware originally supplied by GIVI with the mounts, and that this is for fitment with the stock exhaust. My impression was that the installation was much harder or impossible with some aftermarket exhausts.
If you get the top mounting system installed, I think you will see how the side mounts attach to it. On the side cases, the only anomaly I found was that there is a supplied short metal tube that is supposed to connect the left and right side case racks back by the license plate. I could never get mine to line up perfectly. Half the time I used a substitute "connector tube" I cut from PVC tubing and painted black, and half the time I didn't use anything to connect the racks back there. After using the luggage system for thousands of miles I found it really didn't make any difference because the rest of the fitment system is very strong.
I hope some of this helps you. If you have any questions, let me know....maybe someone will supply the actual instructions....