When adsense asks you - if no google ads are available what do you want to do? I chose, Show ads from another url, and put in yahoo.com ? But I don't understand how that works. What URL would I use to get paid.
You don't need to fill that. Just choose the ad format.customize the colours and click on 'Continue'.
when i try and leave it blank it wont let me! it says must enter a valid url, one of them must be chosen, the last one is fill with a solid color
If you don't participate in an other advertising program choose "fill with solid color (it will be the background color of your page or the table you placed the adsense code)" or "show public service ads". If you are participating in other ad programs like adbrite or yahoo you can place the affiliate url that makes your ads from those companies appear where adsense is shown normally, so if they have no ads for your page the adbrite or yahoo ads will be shown automatically as long as Google is not able to place their own adsense ads there.