Okay, so imagine you have a toy car that you really like. You play with it all the time, but then one day you notice that it's missing a wheel. You really want to fix it and make it look perfect again, so you start adding all kinds of extra, fancy decorations to it. Maybe you put extra stickers all over the car, or maybe you glue on some sparkly gems. But even though it looks nice, all those decorations don't really serve any good purpose. They don't help the car run better or faster, and they don't make it any more fun to play with.
That's kind of like what people mean when they talk about "ornament and crime". It's a fancy way of saying that sometimes we add extra decorations to things that don't really need them, and those decorations don't actually do anything useful. Some people argue that this is bad, because it wastes time, money, and resources that could be put to better use elsewhere. Plus, if we focus too much on making things look pretty instead of making them work well, we might end up making things that don't work as well as they should.
Of course, not everyone agrees with this. Some people think that decorations are important because they make things look beautiful and make us happy. They argue that it's okay to spend time and resources on things that don't necessarily have a practical purpose, because they add value in other ways.
So, the bottom line is that sometimes it's good to have decorations, but sometimes it's not. It really depends on the situation and what you're trying to accomplish. But at the end of the day, even if something looks really nice, it still needs to work properly in order to be useful.