You have to do some reading as outlined above. And it takes some time to learn and maybe some testing as well...
There are Swedish forums for this also (try speedcams.se)
In short there are a few methods to load the maps into your gps.
If you have a gmapsupp.img just copy it to the folder /garmin in your gps and your done (unlocking can be neccessary)
Or you can install Mapsource to your computer and load the maps from Mapsource to your gps.
And there are other methods also.