How the vote works
The vote happens before a match, in the lobby: three maps are on offer and the lobby picks one. The official NEW MAPS announcement describes it as voting between three different maps before every match, running alongside an update that added maps and words.
What that means in practice is one decision per round that no single player controls. You do not need to learn a build order for each map; you need to know, in the first seconds after the map loads, where the height is and where the water is.
What a map changes for you
The map decides which answers are available, because the answers to this game's hazards are positional. Water hazards are answered by height or by going underground; the floor hazards are answered by getting off the floor; hunters are answered by open routes rather than corners.
A map with tall climbable structures offers the water answer. A map with fewer of them narrows your options. This is player judgement, not an official statement: the sources used here do not publish a terrain comparison for the three maps, so no map is rated better than another on this page.
Per-map events
The announcement says each map carries events that can only happen there, which means the vote also decides which unusual events you may meet. It does not list them, and this site will not invent a list to fill the gap.
The one thing worth knowing is that these events do not depend on the Writer's turn: they are the map's own pressure, which is why watching the island matters as much as watching the chat box.
What is not published
This round of research did not find official names for the three maps, a terrain breakdown per map, or the per-map event list. The gap is in the material surveyed, not a claim that the developer never published it — nobody should read this page as "these things do not exist".
If you are deciding how to vote, the honest position is that you are choosing between three unlabelled terrains until a source names them. Vote for the map you have learned, and check the map at the start of the round rather than assuming the layout.