GCSEs, General Certificate of Secondary Education have two uses, the student take them as formal exams that help them get to the next stage of education.
Schools also use them for their 'Progress 8' report - this is suposed to be the top 8 subjects of all children who take GCSEs.
THis is why the compulsory subjects are maths, English x 2 (lang and literature) then the 'ebac' subjects whit are the subjects the government thinks everyone should take, so extra science, a humanity, a language or computer science. The last three 'buckets' are a free choice.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/285990/P8_factsheet.pdf
What I hate about progress 8 is that not all students are even, when I was at school under the old system English and Maths were compulsory (as was RE as it was an RC school) a language was pushed and then the other subjects were a free choice so if you were really good at art you could take s many art subjects as you school would allow.
The sylabus is determined by the exam boards and schools chose the board(s) they want to teach, do for computer science lots of schools use a Welsh exam board even though they ar not in wales.
So all children sitting GCSE computer science with that board they sit exactly the same exam, at the same time as every other student taking GCSE computer science with that exam board.
GCSE grades 1-3 are a 'level 1' qualification, 4-9 are a 'level 2' qualification or a 'pass'.
As PP have said chilldren take 8-10 subjects.
Some take subjects that are not GCSE but are coursework based and again can get a level 1 or 2 pass. These are often TEC but there are some others.
At 16 after GCSEs children have to be in work, training or education. Very few take the work option.
VI forms are normally year 11 and 12 attached to a school, children may stay at their own school or go to another one. Sstudents can also go on to an FE college.
VI forms usualy teach A Levels - these are the exams that get you in to uni, but there are other courses, again BTEC but these can be level 1 to level 3.
Three passes at A Level or equivelent is considered a 'Level 3' qualification and this is what gets you to uni but also is a ualification in its own right.
FE colleges also teach more practical subjects eg mechanics, art, hospitality, catering, car maintenance etc. I've worked at two that have the inside of an airoplane for students wanting to be flight attendants.
I've also eaten in restraunts run by students on catering courses and had my hair cut by a student.
So if you have 10 grade 9 GCSEs you will probably be heading for A Levels. If you have a couple of grade 4 and 5-6 grade 1-3 you will be heading to college to do a level 2 course, and you will have to resit GCSE English and maths.
If you don't get any grades you would start on an entry level or level 1 course.
You can progress from level 1 to level 2 and on to level 3 so you would be at college until you are 20 and then go on to a career or go to uni.