It's a big adjustment going from second to third year. Especially at first, you'll probably feel a bit lost. There will be a lot of "mechanics" you just aren't comfortable with yet, and it won't be immediately clear how to get to the level you'd like to be at. There is, as has been pointed out, a lot of downtime on some rotations, which you'll learn to use effectively as time goes on, but at first will leave you feeling really useless. You'll also have an unclear role on the team and there will be some difficult interpersonal challenges to negotiate. All of this can be discouraging. On top of that, you'll meet some people who will purposely discourage, embarrass, or shame you.
However, you're also going to meet some wonderful role models, discover what specialty you're going to go into, and define what kind of doctor you're going to be. You will have some of the most rewarding experiences this year -- seeing and perhaps even touching the beating human heart, delivering a baby, listening to the life story of a dying patient, and more.
A couple of pieces of advice to make things as rewarding as possible. First -- always do an HONEST history and physical [it may not be complete in some settings]. Depending on the service, you'll find yourself rushed and everyone around you will be cutting corners, and you'll be tempted to do the same. As an example, an honest abdominal exam in the emergency room patient with the sudden onset of abdominal pain includes checking the hernial orifices, even if the patient is rude, smells bad, is visibly intoxicated, or vomits on you. To do this, you may need to get a patient who was triaged to a chair in the hallway into a bed in a room. Some of my most rewarding moments were the result of a good H&P on services where everyone is extremely busy -- catching a yeast endocarditis because I really listened to the heart the day a patient was going to go home that day, or finding an incarcerated femoral hernia because I "borrowed" a bed in which to examine my patient, or helping find the source in a bacteremic patient because I was the only one who knew that they had a MedComp [central line for dialysis] in place when the teams changed over. Second piece of advice, talk to everyone. You'll be much happier (and you'll learn more) if you call the cardiology consult yourself and find out what they said and get any questions you might have answered. Going down to radiology to see the images with the radiologist is a nice break from the hustle bustle of the wards, and no one can fault you for it (in fact, any but a complete a$$ of a resident will think better of you for it). The radiologist often likes having you there because they get to hear the clinical story, which improves their ability to read the scan. Hearing from a patient how they found out they had cancer, or learning that the patient still hasn't told their children, will connect you to the therapeutic experience in a way no amound of reading about the various chemo regimens ever could. Last piece of advice -- master the mechanics (a.k.a. scut). It'll leave you free to do the stuff you came here to do.
In short -- the best of times and the worst of times. Some rotations are just painful, others hard but exhillerating, and others like a vacation. Try not to get discouraged by the initial disorientation you'll probably feel -- these are very rewarding years ahead.
Best,
Anka