Hi ST,
Colour calibration is really a big thing and I think it's possible to get a degree if not a diploma to understand it!
Think I can safely say not many here really understand the full process... For most, it's just a matter of trial and error and being satisfied with whatever results they can get, taking into consideration $ especially. (No offence to anyone as I've been reading the various posts here for some time here and seems like there are always variations or ambiguities. I'm struggling myself.)
The Spyder thingy can only calibrate your monitor. It will not ensure that your prints will agree with what u see on the monitor. Essentially, the device sets a sort of standard if you like and if you go round with it and use it on 10 different monitors, all of them essentially are set to the standard colours. It's like all of us may have watches but that does not men everyone of them will read the same time to the very second. We need to synchronise the watches with any standard clock for eg.
Printer calibration is trickier and you need another device to do it. Esentially, you need to print out a test colour chart (another standard) from your printer and use the device to let it know how your printer is printing. Then you will have a created file that you will use everytime you open your images and b4 you you send them to the printer.
These devices are not cheap. For eg, the Spyder alone can cost at least $350(???) brand new. May not be worth it if you're not really fastidious about 100% accurate colours. Even then, some say it's not as good as other brands which already cost $600 or more.
For printer calibration device, the price is simply nuts.... At least $1K I think. Please correct me if I'm wrong for those who know the details...