I want to join the army but...?

Hey, im 15 and i have spoken to the army careers office about 2 months ago, i really would like to go in infantry, i have thought long and hard on this decision im all ready training to get fit and it really feels like the right job for me although i did want to learn a trade and come out the army with something it doesn't seem right i really want to join the infantry, but my questions this how would it work i have been watching the news lately and have seen the US and UK are bringing troops out, so if i join next year would there still be an infantry even if i don't get sent to Afghanistan? could i still do all the training, and how long will the troops be out there for?