I'm not sure about Sweden, but in the UK we have two different kinds of supplimentary lights:
Fog lights - Have to be positioned within a specific area (a maximum of so many cm from the ground and so many cm from the outside edge of the car.) They must be wired so that they can only be used when the side lights are on (some run only when dipped beam headlights are on) and they must be independently switched from inside the car.
Spot lights - Can be positioned anywhere on the car as long as they're forward facing. They may or may not be switched from the inside of the car, according to preference, but it must only be possible to switch them on when main beam headlights are on.
Wiring for both types is similar. You'll need a relay, a fuse and some wire, all rated appropriately for the wattage of the lights you plan to use.
Wire the body of the lights to the vehicle chassis. Do the same with one side of the relay
. The other side of the relay
goes (via the switch if you're fitting one) to either the side light circuit or main beam circuit, depending on which kind of lights you're fitting.
Then run wire straight from the battery positive, through the fuse and into one side of the relay's switched contacts. Take the output of the relay contacts and run it straight to the positive of the bulb on the first light, and along again to the positive on the bulb of the second light.
If all is well, you should now have working lights!
Edit: I should also have mentioned that fog and spot lights have very different beam patterns from each other. Be sure to buy the right ones.