Applications to Specialty are generally co-ordinated via the Oriel system which handles all applications for specialty. It is important to note, however, that there are differences between the 4 NHS Authorities (England, Scotland, Wales and Northern Ireland) for many specialties. Therefore you need to check the most up to date information regarding applications for the year in which you apply.
All information regarding specialty applications, including to General Practice, is released on the Specialty Training website. The site is generally updated for each recruitment year prior to the application process opening.
You can submit an application for each specialty, although specialties differ in the number of training areas you can preference. It is important that you are aware of the process for the specialty or specialties to which you wish to make an application.
If you are considering training overseas, then you may wish to look at the information which is detailed on the Health Careers website regarding training/working overseas.