Okay, so imagine you're walking outside, and you hear a lot of noise. Maybe cars honking, people talking loudly, dogs barking. That noise is called "le bruit" in French. Now, picture that same place, but there's also a bad smell in the air. Maybe it's garbage, or something else stinky. That bad smell is called "l'odeur" in French.
So, when people talk about "le bruit et l'odeur", they're talking about how there's a lot of noise and bad smells in a certain place. Some people might complain about this because it's not pleasant to be around so much noise and bad smells. However, other people might not mind it so much, or even think that it's just a part of living in a city.
Basically, "le bruit et l'odeur" is a fancy way of saying that a place is really loud and stinky.