Welcome to the Org forums stlcard3. At least you figured out how to invade our forums.

To invade, you need chain of ships from your Port province to the province you wish to invade. That chain can be broken by an enemy (or soon-to-be-enemy) ship. If you have an unbroken chain of ships, all coastal provinces you can invade (move to) will by highlighted in white along with the neighboring provinces that are normally highlighted when you move an army. I hope that was a clear enough explanation.