You don't. The game will decide when a situation arises that allows a vote. It then provides you with a pop-up to vote. For example: If a full member of the AP (Mehmed) is at war with a non-member (Shaka), after a few turns, a pop-up will be presented with options like "Stop the war on Mehmed" or "All members declare war on Shaka". Trade embargo resolutions often pop up when trade is occurring between members and a heathen state. Also, if there are members who aren't trading with one-another, you might see a resolution pop up: "All members open borders." There are plenty of others, but the AI assesses the current status of the game and presents you with resolutions situationally.