How to i get in the army?

hey guys im 15 ( almost 16) and the time to select my year 11 and 12 classes has come, ive thought long and hard about what i want to do and one of the main things i would like to do is join the army, but i dont want to be just a basic soldier, i want to be a sniper ( i don't know what they actually call it) and i was wondering what you need to have to get in ( and yes i know you need to be fit im working on that now i was 20 kilos over weight for my age, now im 15kilos overweight, but im getting there. anyway if anyone knows what you need to be able to do this, i would love to know, and a bit more detail on what you actually do in this type of soldier. ps, i dont want anyone saying i shouldnt join the army because its dangerous or im to young to be thinking about this kind of thing. this is what im interested in and this is what i asked about, so yeh. thanks :)