Maths, English, Science, Humanities, PE, Religious Studies, Language, Art, Music, IT, maybe some other depnding on the school (Drama, Dance for example) generally taught at all secondaries for the first three yeasr (years 7-9), age 11 to 14.
Exam (GCSE) subjects usually selected in year 9 to be studied in year 10 and 11. Some subjects dropped at this point, but Maths, English, Science, PE and RE still compulsory (the latter two don't have to be studied to GCSE though).
NB Some schools start GCSE courses in year 9....
A reasonable able child would typically do 10-12 GCSEs.
Usually theyare taken over twoyeasr (10 and 11) though some schools might start some a year earlier, and maybe take some a year earlier.
A Levels are years 12 and 13. Taken at 16+ years old, taken over two years. Examinied at the end of first year, and student get an AS Level. 'Cashes' in that AS if they continue the subject into the second year to get a full A Level.
Typically students do 4 subjects at AS, and continue with 3 in the second year.
HTH