Normally, you would attend NSI where you have a "knowledge" book that you are responsible for memorizing. This includes everything from Chain of Command, to ranks and fleet structure. Seeing as NSI has been canceled due to the ongoing Covid-19 epidemic, you will only attend an orientation at your unit which varies entirely depending on what unit you are at.
Freshman year (or 4/C year) itself is very dependent on what unit you're going to be at, as each unit functions differently. That being said, there are a few constants. The first NROTC class you will take will be "Introduction to Naval Science" which is a standardized curriculum across all NROTC units, and it is built around learning rates, creed, and other basic functions of the Navy/USMC. In the spring semester, you will take "Sea Power in History" which varies more from unit to unit, however, it's essentially an American history class from the naval perspective.
Leadership positions for freshmen vary widely between units as well. At some of the larger units, you may not have an opportunity for any leadership positions (or "billets") until you're a 3/C or 2/C. At some of the smaller ones, you may have the opportunity for jobs such as PAO (social media/photos) or ACAD (tutoring/academics), or even platoon commander.
Overall, 4/C year is a great time to learn the ropes/transition into college life. Although NROTC should be a focus and is certainly important, don't forget that there are also plenty of opportunities outside NROTC, leadership, or otherwise.