Two questions in one!

What do you do with your eurail pass when on a train where, presumably, someone will be by to check it? Leave it in your money belt where it is the rest of the time and dig it out, or have it out temporarily in your day wallet/bag and then stick it back in your moneybelt the next time you go to the washroom, or what? How does a eurail pass work anyway, do you just waltz onto any train (that doesn’t require a reservation/supplement) and then show the officials your pass when they come by?

How do you lock your backpack to the baggage thingie? Do you use a long lock (the proper name escapes me) so that you can lock whatever permanent part of your bag there is to the train thing? I ask because my backpack’s straps and everything that would be long enough to wind around a metal bar and lock back onto itself is detachable with hooks and snaps and such, so I’m a little confused.

Hope you’re not too bored by my naive questions yet, I leave in 2 weeks for my first ever backpacking trip, so trust me, there will be a lot more!