How does this button work?

Until now, the highest denomination YoVille offered you was the 1000 trade button. You would have had to click on the 1000 button ten times to get to the 10K value. But from here on, its going to be an easy, one click process!

Also, now you can only click on Agree to trade if there is an offer made by the other party.

If there is no offer, it will not be possible to click on agree. This is to avoid scams and making trading fair for every player.