When the editor starts in the future, tips pointing out features of the editor that differ from the Firaxis editor, or more efficient ways of using the editor, will appear here.
For now, you can choose File -> Open to open a scenario. Once you've opened a scenario, all the various rule section tabs will appear, including the map.
Nearly all features of the Firaxis editor are supported. Most are fairly easy to find, but a few may be in different places. Of particular note is that you right-click on a list of units/technologies/etc. to add/delete/rename, rather than having buttons for these. Screen space was at a premium on some tabs back in the day!