It opens on a new game screen and a map you have not seen yet. Settle, and the familiar loop starts: tiles produce, the city grows, and research opens the next thing you are allowed to build. Turns are yours to take at whatever pace you like, and the game keeps its own save.
This is a browser sized take on the empire builder rather than a full one, so the tech tree is short and the diplomacy is thin, and it is better for it: a session ends in an hour instead of a weekend. What survives the shrinking is the part people actually play those games for, which is the first twenty turns, the argument with yourself about where the second city goes, and the moment the map stops being empty.