What am I supposed to do exactly?
Once you know your Major sit down with your advisor and ask them to draw out (write out) a small map or list of EXACTLY what classes you must take to get the degree you are seeking.
Do not be shy to ask this, this will save you a LOT of time spent on worrying whether or not a class is actually necessary for your Major/Degree. And you will also save yourself from having to visit the advisor repeatedly to figure things out; along with a bunch of money you won't be wasting on "worthless" class (in terms of Degree requirements).
Personal Experience:
I actually did this step on my first day of classes at the University I transferred to. Since I was a new transfer with more than 60 credits I had to make sure the classes I had taken in the previous school counted, and if they didn't then I'd have to know what exactly I have to do in order to make up the credits.
The advisor actually gave me a document that listed all the classes I had taken and need to take: she marked the ones I had already finished and let me know which remained. So don't be afraid to ask, they want you to ask.
Knowing where you're heading will definitely help you sleep at night (it did for me at least).