To make a map, start by selecting a size on the first slider. That will unlock the next step, which will add tectonic activity. Click that as many times as you like before adding water to the oceans by adjusting the Ocean slider. Once you're happy with that, select a hemisphere and fiddle with the climate of your map.
Clicking the last button will (after a moment) take you to the selection panel where you can pick a group of people to play in the game.
Once you select a people, you will be taken to their home tile where you can see various details about them and their home. Mouse over the different populations in the People panel, the sites in the Land panel, and the rites in the Worship panel for more details. You can click on the "Next Season" button to see what happens to them.
Eventually, you'll be able to actually, you know, do stuff, but that hasn't been coded yet.
To start over, just reload the page.