I'm actually American so I don't know the specifics.
I do know it goes
Primary School
Secondary School
College
University
They have no real "high school."
Here's the most common (state-funded) route in England and Wales:
Nursery > Primary School > Secondary School (=Senior School) [> University | Professional College]
Most pupils sit their GCSEs (school exams) at age 16. If you wish you can then take 'A-levels' (advanced school exams), usually at age 18. Some people go to 'sixth-form colleges' to do their A-levels, others simply continue their schooling at the school where they also sat their GCSEs.
Of course, there is also the private route:
Pre-Prep School > Preparatory (Prep) School > Private/Public School [> University | Professional College]. Private schools do not have to offer GCSEs. Instead, they can set their own exams.