Stupid questions are the best questions! (And, i don’t think it is stupid).
A-Levels are subjects which usually broaden your knowledge of subjects learnt at GCSE, and set you up for more university-based topics. Depending on which you choose, there my be some things entirely brand new, and that’s okay! A way to help you understand what they consist of, in more detail, is by looking at some specifications. Science are typically AQA, but it depends on what college/sixth form you wish to attend.
I hope this helps!