Go on mathswatch because they have really good and simple videos, or use the Dr. Frost powerpoints or hegartymaths on youtube, whatever resource you prefer. Make sure you understand each concept fully and that you know the steps for things youre meant to work out. The main thing about maths is understanding, because then you can apply concepts in a wider sense. Afterwards go on youtube or websites and watch videos of people going over questions from that topic (eg mathssaurus, therea some other recourses but i forgot what they were, will link if i remember) and answer them with them. See where you go wrong, it could be one small silly mistake at the very beginning that causes you to lose all the marks. Then just practice. Just keep doing topic packs until you feel very confident. It could be a long process but it’s alright. Just dont loose your track. Also if youre really lost try asking youre teacher or a friend for help. Good luck!