Yeah that's the one you're in, I think the actual moves are very simple, armies move one on land, boats move one on water or water-adjacent land. The trick is that everyone moves at the same time, and you need to convince your opponents to help you defend or attack.

Also, they seem to have a strategy forum if you want to read up: https://www.playdiplomacy.com/forum/viewforum.php?f=16

From the website, here's the game rules: https://www.playdiplomacy.com/help.php?sub_page=Game_Rules

And here's a series of instructional videos they recommend: 1, 2, 3, 4