My basic understanding is along same idea as what jl123 is saying but with it now being broken down as combat engineers (think sappers - guys that go blow stuff up, clear obstacles, etc.), vertical, and horizontal units. Vertical and horizontal are both construction type units with horizontal focusing on things such as bridges and vertical on infrastructure. You might not have a lot of control over where you're going, but you can help guide this by trying to be stationed at a unit that has the type of mission set you are looking for.
Any 2LT, or officer job, you get in the Army, you're going to see a lot of excel. Your job as an officer is to manage the personnel under you, making sure they have the resources and direction they need to accomplish the unit's job. There are very few specialties in the Army where your primary job as an officer will be the doer of the unit. That doesn't take away your responsibility of being a technical and tactical expert in what you are doing, but you will have your NCO's that have much more experience and practice in the tasks your unit is trying to accomplish. Your job is to keep that unit performing and directed onto the task at hand.
To give an example from the Aviation branch, as an commission officer I am fully expected to be able to fly the aircraft and be a full functioning crew member to include being able to serve as the pilot in command of the aircraft, but at the same time, my primary focus should more be the air mission commander type (the overall mission of the unit versus the accomplishment of the tasks of the individual helicopter that the pilot in command is ultimately responsible). That's where our Warrant Officers come in. They're the technical experts and good ones will typically have much more flying experience than senior officers.
I don't say this to make it sound like officer jobs aren't fun. You still will do a lot of very, very cool stuff in whatever branch you end up but there is a mindset that you will need to get into of what an officer's job is that you will learn through USMA/ROTC/OCS and continue to build the longer you have been in the Army. Good luck, and hope it works out!