What word do the Japanese use for.....

Rubbish. Not as in ゴミ but as in something like "That film was rubbish"

"kuzu" is a word used to refer to useless, worthless things.

But when we refer to movies, works of art that were no good, we might say "dasaku," in the sense of a complete flop.

Why is that Japanese teens seem to use ww alot? They seem to use it if they're saying something like naruhodo. I also see it when I'm speaking online to people, like they'll say it when I tell them that we're having bad weather in my country

"w" or "ww" on online chat? That seems to be similar to "lol" or ":)" (not necessarily laughing at something, but including smiling, grinning, snickering, etc.)

Oh yes online. Don't know why I didn't say that

www = warau = to laugh/smile