Then you should do well!
Nothing online "should" be confusing if you already understand the basic game.
Each Diplomacy website is a bit different and has it's own unique traits but all are pretty much the same at the core. I would caution you to pick your first game with a bit of care, make sure the deadlines fit your schedule. If not a standard game (as you already know the basics) be sure the game you pick is interesting to you and you understand all the variant specific rules changes. And then in general terms, do not be shy! Think of this as a face to face game with total strangers ...maybe you are in a tournament setting? If it were face to face (FTF) then you would obviously be talking to these other people. Same here, write the others early and often, what you say is hardly different from FTF but you do have time to THINK about what to say, how to say it, etc. You are not as rushed and you can thoroughly plot and plan. Read into what others reply to you and just as if this were a ftf game, excuse the language as some may not speak English as a first language (many more than you might think). Your first message might be a generic hello with your name, where you live, what you do, how you came to know the game, and of course some general plans. The preliminary "nonsense" would be similar to a face to face game where you are sitting around the board as you set things up. Be certain to write ALL your neighbors as soon as possible, as far as the next tier out (depending on how large the game is) depends on you but always always always write your neighbors and try to even be first to do so!