Firstly what exam board do you do? I do edexcel so what I say might not apply for you but I would generally say that understanding the content is easy.
Go on GCSE pod and watch videos for each topic, make flash cards for 1)things you don’t understand and 2) key dates. When I was in year 10 I would make such stupid flash cards for information that is super easy to understand which wasted my time. After that, either make a mind map or a time line.
As I’m not sure of your exam board or which topics you study I can’t really give you exact advice for exam practice but I would say overall really try and understand what the question is asking you. Like for my exam board we have 4 markers which require 0 knowledge or very little knowledge but many people lose marks as they don’t actually know what they are asked to do(I can help you with that if you’re unsure).
Look at the mark scheme for each type of question, it will tell you how the marks are broken down.