I believe that your local education authority will provide free classes for GCSE English and Maths, at evening classes.
Ask at your local library.
Don't recommend you do both in the same year.
Once you have 'conquered' those two important basics, have a look at the other subjects - whatever you are interested in: History, Geography, Art, Music etc.
Take your time and you will get there, and you'll have a great sense of achievement.
Investigate now, if you plan to do the Maths and English. I think the classes start in September.
Off to the library tomorrow, and the very best of luck.
Let us know how you get on.