If for some reason you would like to attend an opera performance at Milan’s Teatro alla Scala (even after reading my other posts about it, LOL), you of course have to buy a ticket, which can be a problem since performances are generally sold out weeks or months ahead of time.
One way is to line up (well in advance of the date you want!) at the box office in the Duomo subway station, as these young folks are doing, though I suspect they are eligible for student tickets at reduced prices.
Or you can try to get one of the 140 numbered gallery tickets that go on sale on the day of the performance. There are elaborate regulations for getting one of these tickets — only one per person. I’ve never done it, so I can’t speak from personal experience, but basically you have to line up at the ticket office in Via Filodrammatici (not the one in the subway station) by 1 pm to get your name put on the list, and then be there again at 5.30 pm for the roll call and sale of the tickets. And then be back at 8 pm for the performance, so it’s pretty much of an all-day procedure.
Another way is to spend several hundred Euros and buy a black-market ticket from one of the scalpers who hang around the entrance to the Scala Museum every afternoon. These are shady-looking characters who talk out of the sides of their mouths, wear their hats down over their eyes and have several tickets fanned out in one hand (I’m not making this up).
Or you could buy your tickets on the internet, as I did. After lots of clicking around I finally managed to snag tickets for two different performances.
They have a list on their website of when each opera goes on sale (about two months before the premiere), and when I tried to access their website at 9 a.m. Italian time on the first day I kept getting notices saying they were overloaded and please try again later.
When I got in an hour later there were no tickets left, BUT. . . I discovered that the trick is to try again six hours later, because anyone who has reserved a ticket has six hours to pay for it, and if they don’t it goes back on sale.
So at 3 pm Italian time the number of available tickets on different dates starts changing from 0 to 1 or 2 or whatever (the record was 13 while I was watching), and then back to 0 again a few minutes later. You just have to keep watching the numbers, and when a ticket you want shows up on the screen, pounce on it. Of course it helps if you live in the same time zone and have nothing particular to do on that afternoon. If you live in California, for instance, you would have to get up at six o’clock in the morning to do this.
(This was the procedure that worked for me in 2008. Is it still the same today?)

More people queuing in the Duomo subway station
http://www.teatroallascala.org/en/
My photos in this post are from 2008. I revised the text in 2018.
Next: Theater Museum of La Scala.