How do speeding fines work?

The fine depends on how much over the speed limit you were going and whether you were driving in town or outside town. It's stricter in town because there's more accident risk. For smaller violations (say up to 10 km/h over), you pay relatively little, maybe 30-50 euros. The higher you go over the limit, the more expensive it gets - at 20-40 km/h over you could be looking at 100+ euros, and at even higher speeds it quickly runs into several hundred euros.

On top of the actual fine, you can also get points on your license. That's really important to know because once you hit 8 points you have to surrender your license. For relatively minor violations (up to about 20 km/h over) you usually just get the fine without points, but anything above that and you get points added on top. Some violations can even get you a driving ban for a while - that mainly happens in really serious cases.

The speed measurement itself has to be correct too, otherwise you can contest it. There's a certain tolerance that gets deducted, so if the police measured 65 km/h, they subtract something internally before they calculate the fine. You find out whether you have to pay by mail - that's when the fine notice arrives.