Scientists pick an area of science to become really good at. So I decided to study chemistry, and I’m now specialised in materials chemistry which is a small part of the subject. Most scientists are experts in a very small aspect of science.
Scientists study things by forming hypotheses and designing experiments to prove those hypotheses. This might involve working in a laboratory, working outside (like studying animals in their habitat), and also involves writing up the results of the experiments so that other people can find out what they’ve done and discovered. Science is all about discovering new stuff about our universe.
Actually, stuff you learn in Biology, Chemistry and Physics may seem unrelated to each other. But as you go along, you will realise that these sciences are all very much connected with one another. In fact, more and more research these days are not just focussing on one area of science. To be a successful scientist, you will need to know more about the other sciences as well as your own field of research.