This is a very broad question. Once you graduate from Computer science engineer you will usually join a company as an developer/programmer, or qa engineer. There are might be some opportunity in other fields as well like project management or technical writer, or architect. You can also become a manager or a tech leader for your team. As to exactly what do they work on its a very broad question to answer. It totally depends on what company does, or what a specific organization or the team in the company does. There are some companies like Infosys, Wipro, TCS etc. which are large MNC companies but they usually provide technical services to other large companies like Apple, Cisco, Microsoft, etc. Then there are some other companies which are product oriented companies who build actual products like Apple, Cisco Microsoft etc. E.g Apple will make iphone, apple tv, mac etc. Cisco will be making routers, switches etc. That does not mean that product companies do not hire. They also hire talented people.
Most of the time a team is assigned some projects. The projects are broken down in various small goals and engineers are meant to work on these small goals. The goals could be anything based on your background and expertise. Eg you might have a background in UI, and might be asked to build some websites or some UI for some Phone app on IOS or Android.
The courses that you usually study in the computer science program will help you build a foundation. Your foundation needs to be really strong, that will help you in your everyday work while you work in any tech company. The basics or foundation will never change even after you work for years in a tech company.
So study well in your college. Good luck.