Oxford and the Collegiate System
There are a million reasons why you should apply to Oxford - if you're likely to get the grades (three A's at A level or equivalent) then you should definitely give it a go.
Tourists often come to visit and wonder where they can find the famous university. There is no main campus, nor specific areas of the city, but dotted all around Oxford city centre is where you'll find colleges, departments, museums and libraries which all comprise the university.
Oxford is a bit different from other universities because it's made up of colleges and departments. There are 38 different colleges, and each Oxford student belongs to a particular college where they live and spend most of their time. The departments handle the subject courses, and bring together students from all the different colleges to have lectures/classes/seminars/practical labs together.
It's a great system because colleges are quite intimate and it's easier to get more involved with various things and meet lots of people studying different subjects.
The number of students accepted and the courses available vary from college to college... see here for a list of courses offered at each college.
Colleges
The college system works on the principle that you're more likely to get something done if you do it yourself. Hence-why that while each College is part of the University of Oxford as a whole, it's also an autonomous body in its own right. Each College houses it own population of students, tutors and staff and each will have its own accommodation and dining facilities as well as its own unique traditions and architecture depending on whether it was built by Henry VIII or some mad architect in the 50s.
Because each College is independent and different from another, it means that not all Colleges will offer all the same courses. St Anne's has a rule that it'll only offer a course if it has a tutor employed to teach some areas of that subject - and as one of the bigger Colleges in Oxford, it therefore offers most of the courses you can possibly do. Make sure you check before you apply though...
With all that said, while in your first year (and every year of your course afterwards if you choose St Anne's) you can live in your College, because no College can have experts in every field of a specified subject, you may find yourself doing tutorials in other Colleges, such as Exeter, Jesus, or (heaven forbid) Wadham. Have no fear though - the only reason this happens is to make sure that students get the best possible teaching, and it's good to experience another College's culture every so often. Even if it just makes you glad you're at St Anne's.
Departments
Your Department, or "Faculty", is responsible for the overall co-ordination of your course, sets your exams and syllabus, and depending on your subject may be the main provider of your formal teaching, or merely an occasionally helpful resource to supplement your College teaching. The Science subjects will generally find themselves visiting their Faculty for lectures and practicals (e.g. experiments). A subject like History, on the other hand, will more than likely spend more time in the library and receiving teaching from their College while only visiting their Faculty for the occasional lecture. It really does greatly depend on what course you choose!
Libraries
Oxford prides itself on its many Libraries. Whether you will ever visit a library and read a book will depend again on the nature of your course, but most people will find that they either hover between the College Library or their Department Library, if only to find a quiet place to work.
The College Library at St Anne's is brilliant and full of books for pretty much all subjects and is updated throughout the year to make sure that you often don't have to walk more than 5 minutes from where you live on the College site to find the right book you need. On the occasions that you need something slightly more specialised or just fancy a change of scenery, most Departments have their own libraries or share part of the massive Bodlean Library, which is situated in the middle of town. The LawBod contains all the law books ever published, while the English Library has its own site as well. The sheer size of many of these places will at first make you feel very small and lost - but all of them have dedicated staff on hand to make sure you find your way around and to give you hints about where you might find something useful for that essay you have due in for the next day.