"now we're onto something."

I watched the movie, Bucket List

While watching it, there was an expression, "now we're onto something"

The context is like this;

Carter made bucket lists, which are the ones you got to do in your lifetime.

But the lists were quite weak, so Edward said like this, "I got one. All right. How about skydiving?

(while writing it down) now we're onto something"

I know what the meaning is a little, but I want to know the exact meaning and in which situations

I can use it.

Thanks in advance.