Rat's nest in Eagle

I was wondering how is this function working in eagle that fills the spaces of the pcb with the ground signal when you hit the ratsnest button..

Couldn’t figure out how to do it in my boards.

Bye, uclaros.

It´s stated in the tutorial:

First, hit the polygon button (the active layer must be the one where you want that filling). Type in your ground name (e.g. “gnd” normally). This links the polygon to the ground channel.

Next draw the polygon (normally just make a rectangle including the whole board).

And hit the ratsnest: Voila! Filled spaces.

Have fun!

Thanks pay_c!