1. There are a bunch of drop-down menus in the game that you can use to select your action. Something like
"The army at Liverpool [drop-down: "hold", "move", "support hold", "support move"]". By default, everything holds (like in real diplomacy with CD and all that).
To issue an order, just select the new order from the drop-down menu and hit Update, then the page reloads with another drop-down relevant to the move in question. For example, Move will add "to [dropdown: countries you can move to, including theoretically possible convoys]". Input that information and hit Update again, which will confirm the choice. Sometimes there will be a third one-- convoys require a start and end, for example, and support moves require both a target and the moving unit.
2. Yeah, just open the tab of the country with whom you want to communicate, enter a message, and hit Send.
3. The colors of each individual land territory indicates who owns it, and those colors match the colors of the country names everywhere else on the page. But for reference: Austria is red, England is pink, France blue, Germany brown, Italy green, Russia violet, and Turkey yellow. Neutral territories are somewhere between yellow and beige. As for who owns what units: If there is a little square surrounding the unit that's a certain color, use the color of the square as above to see who owns the unit (this occurs on sea and in a foreign country's SC during the spring); otherwise use the color of the country.
Once you get used to the interface, it becomes really intuitive.