Not much to add. Just 5 or 6 paragraphs!
Americans have lousy lane discipline, especially in the cities. It's better out in the countryside, but you'll still encounter people who insist on the left lane because they're doing the speed limit. "Slower traffic keep right" doesn't apply to them in their minds because they're doing the limit. They don't quite catch the difference between slow and slower. You'll have to undertake to get by, which nobody here cares about anyway. If you're on an Interstate with 2 lanes each direction, you generally want to stay to the right except to overtake. If there are 3 or more lanes, you'll be in a higher traffic area, and lane discipline starts to decline. The more lanes, the less discipline. God Bless America!
If you're very unlucky, you'll catch up to a mile-long gaggle of traffic being held up by some moron in the left lane running 10 under the limit and clueless. Nothing to do with people like that but shoot them, but that just makes traffic worse.
Traffic generally does about 10 over the limit on rural highways, and most places nobody will bother you for 65 in a 55, 80 in a 70 zone, etc.
On 2-lane rural roads, the center line is either broken white lines, or some combination of a solid yellow line, two solid yellow lines, a solid yellow line on one side and broken lines on the other. That's how we mark passing zones and no-passing zones. If the line is a single broken line, or if a double line has broken lines on your side, then you may overtake if you're clear of oncoming traffic. If a solid yellow line is one your side of the center, or if it's only a single solid yellow, then you may not overtake. Generally you find curves and hills marked as no passing like that, but sometimes a congested area will be marked with double-yellow for
miles, and all you can do is trudge through with the other sheep.
If your road has a bicycle lane, it will be a narrow lane marked on the shoulder area with either a diamond or a rider silhouette. If your street has a right-turn lane at an intersection, the bicycle lane will stay to the LEFT of the turn lane, so traffic entering the turn lane crosses the bike lane. Don't pass a bike and then run him over to turn right. It's frowned upon.
Right turns are against the curb, left turns cross the lanes, backwards from the Mother Country. On the freeways, exits are almost always to the right, merging is to the left.
As a pedestrian, look to the LEFT first before stepping into the street.
Carpool lanes are also called HOV, for High Occupancy Vehicles. As stated, they can sometimes remain clear when other lanes are very congested. Even if they are not separated from the main lanes, you can't just merge in and out of them. Many places they are actually physically separate from the main freeway, and take many shortcuts through interchanges and other features.
The mention of motorcycles and lane sharing comes from the fact that in the U.S. the only state which allows it is California. It's illegal in all the other 49 states. Since bikes lane-share in Europe, and filter to the front at lights, it's probably not a new phenomenon for you. Keep the lane difference in mind, though; bikes are not
supposed to filter on the right, only between lanes, but some do it. A right turn into McDonald's in front of an unseen motorcycle could be bad.
Speed limit signs are ALWAYS white with black lettering, and contain the words "SPEED LIMIT." The yellow signs that accompany some curve warnings are suggested speeds, not legal limits. If you drop to 10 because you see a yellow sign that says 10, you'll get shot. Lately many road departments have started using a yellow diamond with a speed limit sign inside it to warn of a reduced limit ahead. That sign is NOT a speed limit sign, merely a warning that there is one ahead, and that it's posted limit is lower than the zone you're currently in. Saying "Reduced speed ahead" was too complicated, I guess.
Stop signs are ALWAYS red octagons with the word STOP. Some intersections will have stop signs for all directions, and it's up to the drivers to just amicably take turns.
At a traffic light there will many times be separate control for the left turn lane. If you get a left arrow, then the oncoming traffic is being held and you may turn safely. If you have a regular green light, not an arrow, you can turn when oncoming traffic is clear. If you have a red arrow on the left turn lane, you MAY NOT TURN, regardless of oncoming traffic.