Hi Donna,
Yeah like wolvesaussie has said, you just follow the instructions online and in the section about how much teaching experinece you have you can download another form which is mainly green (it might be called form B but can't remember) if you want to apply for full registration. Then your headmaster fills it in for you and you sent it off along with your certified documents (which your headmaster can also certify).
If I can do it then it must be straight forward but let me know if you need any more help!!