You get a fine if you're on the electoral roll but were not counted as "having voted". Since we have a private ballot system, you can write whatever you want on your ballot (so you can "abstain" by writing "fuck you all" on your ballot and it'll be considered an invalid vote). You don't get fined for placing an invalid vote, you just get fined if you don't show up (and didn't vote by post and so on).
We have many different ways of voting, so it's designed to be as easy as possible for people to vote (in contrast to what I've heard from Americans). The fines are not that bad for first-time offenders but they're large enough that it discourages people from not voting (the fine gets larger for subsequent offenders).
The rules for voting in elections and referendums are also the same (so the same fines apply).
In the Austrian case I suppose "not at all", but usually compulsory voting doesn't mean that you're dragged to the urn, but that you're paying a fine if you donÄt vote.
We have many different ways of voting, so it's designed to be as easy as possible for people to vote (in contrast to what I've heard from Americans). The fines are not that bad for first-time offenders but they're large enough that it discourages people from not voting (the fine gets larger for subsequent offenders).
The rules for voting in elections and referendums are also the same (so the same fines apply).