Thats a bit vague really. It would be better if you asked your own questions about things you find difficult when revising. Most people on here are American and have no idea what a GCSE syllabus contains. I'm British and I don't know. So if you ask about specific things then people can pass on their knowledge in that area.
General advice would be to find out what exam board you are taking the exam with. Most exam boards now have websites where you can download your exact syllabus which is handy for revision. They also have past papers and mark schemes so you can see exactly what the examiners are looking for for particular types of question. Also if you get stuck on any particular concept when you're revising come here and ask about it, and hopefully someone can clarify that for you.