First of all you will be taking notes within your classes. However depending on your subject and teachers the amount of notes you take will be less than you did in class in GCSEs and they won't be on top of you to make sure you're taking down anything. You could make no notes in class or take down everything that's mentioned but you won't be explicitly told what to take down. There will be frequent gaps in the lesson where you can take down stuff or just twiddle your thumbs, so its up to you to make sure you get all the stuff you deem relevant.
I would recommend buying a A5 or A4 hardback note book for each subject so you consolidate your knowledge after each chapter or topic in your course. For reference in the sciences there about 15 chapters per year per subject. This allows you to review what you've learn't and recognise what you don't quite understand whilst its fresh in your mind. I also find that writing notes in your own words, rather than those from a powerpoint or text book, really helps the learning process. It also makes revising that much more easy because you already done all the learning.
The work load isn't that bad if you manage your time effectively. If you use your study periods effectively you may end up having less teacher-set work to do at home than you did at GCSE's, especially if you do 3 subjects. I did 5 a levels and played rugby 6 days a week and found it not too excessive .
What subjects are you taking.