After a few classes under my belt at college, I feel I can start comparing them to what classes were like in high school.
First off your name will be different. You will either be called by your formal name that your teachers in high school only called you the first day. Even worse, you will be known only by your student ID number. In your freshmen 200+ person classes the professors tend not to care whether or not you show up.
However, there is more flexibility in your schedule. You can decide when your classes start and what you do when you aren't in class. However, if you caught a bad case of "senioritis" while in high school it gets worse. Your parents aren't there to tell you that your math homework needs to get done. In today's world, with all the streaming and portability of television, the distractions are very difficult to ignore. But if you want to pass, you have to find a way to not get distracted every night. You can also decide what classes to take as there is more of a variety of classes to choose from.
The food is different. Not in a bad way but the options are a toss up. There are healthy options and then there are not healthy ones. Mom isn't there to pack your lunch or make you a healthy dinner, so you have to decide to eat healthy or not. The worse part is that you eat the salad and you think you are healthy, then you walk by the ice cream bar and you sneak a little. You can once or twice without feeling anything but anymore you start to see it.
Which brings me to the point of exercise. Some of us (I am one) are former high school athletes. We were at practice five to six days a week. Then we get to college and we decide that we don't need to run or lift like we did in high school. However, with all the carbs that the dining hall food gives us, it would be a good idea to exercise unless you want that 15 by Thanksgiving (which I'm sure most of us don't). It would also be a good idea if you decide that you want to drink (yeah, alcohol has calories).
The college workload is different then high school. In high school, you were in class eight hours a day with, on average, three hours of homework. In college that work has shifted. You are now in class for three hours and you should study for six to eight. It is difficult to do, considering the above package. Don't be expected to be reminded of due dates. The professor might remind you, they might not. It is up to you to know the syllabus and when things are due.
All in all, college is different than high school. It may be harder but there were plenty of people who made it through before us so we can make it.