TBH, once you're through passport control at an external border (for Americans: be sure to take the lane for non-Schengen citizens, AKA "foreigners"

), you can go where you like within the Schengen area without any hassle at the border — except for the fact that some countries (chiefly Germany) have been instituting checks at borders with other EU countries again. This despite these being illegal except if they're temporary and for a specific purpose. (Germany, of course, claims they are. IMHO they should be told to stop it.)
Other than that, if you intend to drive in Europe then it's probably mainly traffic rules and
especially traffic signs you will want to read up on before you go. About the only traffic sign you'll see that's familiar to you, will be STOP. And there will be far fewer of those than in North America, because there pretty much are no four-way stops in Europe. Instead, get over your fear of roundabouts