Creating a Map
To create a map from scratch, start by clicking on Create a Map or New, then Map.
Give your map a name and select a basemap (such as Open Street Map). This defines the map (and hence layers) that your new map will start with.
Click Create Map.
You now have your very own map based on Open Street Map.
Go ahead and play around with the map by panning (left click drag) and zooming in (mouse wheel or right click drag) on an interesting location.
Or jump to specific coordinates at the bottom right of your screen.
To save the map, click on Save near the top right corner of the screen. Alternatively, the dropdown allows you to Save As.
To save this specific view of the map so that it appears just the way you see it in My Library (see below), click on the bookmark icon on the bottom right of the screen. Create a new bookmark (+), give it a name, tick the Default box, and click Create.
You should now see your new map in My Library.
Next: Creating a Layer