The graduate admissions procedure for Oxford University requires each candidate to apply directly to the University. As part of that application you can specify the college you wish to be considered by should you be offered a place by the Faculty. If your application is accepted by the relevant Faculty it will then be passed on to that college for consideration. You can leave your college choice blank (an ‘open' application) and have it allocated to you by the Graduate Admissions Office.
Corpus receives many applications every year and the selection criteria that we apply to considering applications can be found here. The competitiveness of the application process should not put you off. Even if you do not receive a place at Corpus you will receive an offer from another College. See the University's 'Decision timeline' page for more details.