Firstly, you need to contact your schools liason officer who will tell you all you need to know.
Secondly, well done on deciding to do a degree, it offers insurance if the army doesn't work out, or if you are injured etc.
Thirdly, you have had some advice to get involved in cadets and TA. A word of warning. You run the risk of army burn out. If you're commissioned in the TA whilst at uni, you then have to go and start again at RMAS. If you have a good degree, and a good job offer, you may just think the idea of going to learn to iron your kit and polish boots (again)unappealing! If going regular army, why waste your youth playing at what you want to do as a profession anyway? Get out there and do other things. This is also more appealing to recruiters as well. Duke of Edinburgh's award at school, and general viking behaviour at uni.
Fourthly, whilst wanting to be a Para is no bad thing, do not become single issue on a regiment. The Paras may not want you. You may not be their type of officer. But that doesn't mean you will not fit into another regiment's ethos, and actually be far happier there.
Lastly, take care physically. If going infantry you'll take enough knocks. Don't get all army barmy now and wreck yourself. Keep fit, play sports etc, but don't trash yourself.