A subject very important to me when I travel, I found it pretty simple to find and use WCs in Austria. However, be prepared - most of them require a 50 cent coin, well at least for women. If you're a guy there's a good chance you can use the loo for free if you don't need to sit down, if you know what I mean. Not fair, but very convenient. Otherwise you'll need coinage, so hoard and guard those coins. Some of the coin machines accepted bigger denominations like 1 or 2 euros, but I don't think they would make change. And in a busy location like a train station the turnstiles might accept a credit card.
Look for directional signs on posts, but be aware that sometimes there would be a sign and the loo would be a long, long walk away.