When it comes to choosing your GCSE subjects at school, I believe, as a pupil, you should be offered more help and guidance and it can have an impact on what A levels you do, or college course you can sign up to.
If you are really struggling with which subjects to take it is often important to remember which ones you enjoy as you may well find that the job you want to progress to involves these subjects. You should also have careers officer available to you to discuss your options and the teacher for each subject should be able to talk you though what the GCSE entails and if they think it is suitable for you.
Overall do not panic about it, even if you do pick the wrong subject very often you will have a chance to do a similar course at college to obtain the qualifications you need to a job or university.