What is the noise in a wireless signal (wi-fi)

[army20]

Hello

I was just curious about settings for my wireless router, right now I have a signal of -36 (changing) and noise is at -98 (fix).

What is it gonna do if I set the noise at -50 ?

The lower is the best or the higher is the best ?

Also, why there's always a minus sign when tlaking in DB or talking about noise ?

-Martin