It's pretty easy, when is in your country / state time 7pm you will see on right side blue button saying USA, just click there and you should see all spots that were uploaded that day.
Then on every spot will be again blue button which says: ''Vote for this spot'' or some thing like that.
Choose 1 you like and press that blue button and then it will ask you if you are sure you want to vote for this one. And you are done. O and you can vote till 9pm.
O yea and your country needs at least 5 spots to be possible to do this spot of the day thing.
Example: Well in this case you can see ''Bulgaria'' but there will be USA when 7pm will be at you