Hello, first of all, don't panic! You can break down your revision simply. I've just finished year 11, so i'll try give you some of my advice and tips
Firstly, I used
https://getrevising.co.uk/planner to create a revision timetable. It's easy to use and I was able to add all of my extracurricular activities on top of revision sessions. And it's also apart of the student room. I'd suggest writing down all your subjects and then ranking them from one being the one you find the easiest to manage/study and then the eighth being the one you struggle with and you know you've got to work slightly harder on to succeed in.
For science, break down each subject (Biology, Chemistry, and Physics) into paper 1 and paper 2. <- You can do this for other subjects such as history (I think there's 3/4 papers for history) and geography (3 papers).
When you're doing a full day of revision; aim to have at least 4 different subjects on your timetable. Use the 'Pomodoro Technique' to keep yourself focused (
https://francescocirillo.com/pages/pomodoro-technique ). After doing 25 minutes, have a short break and then r
epeat for a whole hour. Once you've completed a whole hour on bioenergetics for example, have another break but this time a longer one. Afterwards, go onto something like maths. You only need to revise a specific subject in till you've fully understood it. Do a test on the knowledge you've learnt before finishing. In addition, when you're revising in the day don't do the same subject for the whole time! This won't be helpful nor effective.
I hope this helps, you're welcome to message me if you need any additional help or support. Good luck