Specifications (they used to be called syllabuses) for examinations are to be found on the major examination board websites. On these sites you can find the full content and requirements for your chosen subject whether it be at GCSE or GCE advanced level.
The examination boards are the awarding bodies responsible for setting of examinations and the issuing of certification in the GCSE, Standard Grades, Highers and A Levels for those examinations in the United Kingdom.
In addition you will also find past papers and mark schemes to help you in your studies. Occasionally you may find recommended text books, examination timetables and study guides.
The major examination boards are: