It's actually pretty simple with Far Harbor - Fallout 4's first major new area DLC (and third expansion overall) - but if you've been away from the game for a few months, you might not know which quest to follow or radio station to listen to in order to find the new content. Bethesda always has some issues on this front, frequently not making it completely clear how to start the DLC quest lines in their huge open-world games like Fallout or Elder Scrolls.
