Oxford interview

Dr Matt Williams' videos on youtube discuss interviews in general.
Each college is a self-governing and (to some extent) self-funding academic community. Each college has its own character, quirks, and traditions. The colleges organise an undergraduate's tutorials (at the college or by arrangements with other colleges) and monitor the academic progress of each student. Each college provides accommodation, meals, a library, social life, sports facilities, and various forms of support its members.
The university provides lectures, other classes, labs, libraries, and sports facilities, and it sets and marks exams and awards degrees.
Some colleges are old, some are new. Some are large, some are small. Some are well endowed, some are not. Some offer accommodation throughout the undergraduate degree. Others ask students to live out in privately rented flats or houses for the second year.
Not every college offers every subject, but most colleges offer all or most of the most popular subjects.
Most colleges have undergraduate and graduate members. Some colleges are for graduate students only. One college is only for academics. One college specialises in mature students.
Good luck!
The best college is almost invariably the college which makes you an offer.

You're welcome. The last Oxford Open Day this year is on 20 September, IIRC. You can also see virtual tours of colleges and of university buildings online.