How to get into a UK university?

Idk if this is the right sub to be asking this but I'm a 9th grade student in belgium and I go to a French speaking school that follows the belgian curriculum (so not an international school) I get mostly As and Bs in humanities but I struggle with science-based subjects like maths and will usually end up with Ds and Cs (50-75%). I still have time but I know my grades are very low and I really need to increase them. Any tips on how to apply and if I stand a chance in getting in anywhere?