Terms at Oxford are short (8 weeks) and for most weeks of the first year you'll have 10 hours of lectures a week in term-time, running from 9-11 in the Mathematical Institute (Maths & Philosophy and Maths & Computer Science students will also have some lectures in the University Examination Schools or in the Department of Computer Science respectively). You can find out information about the first year courses in the Information for Current Students section of the website. The handbooks for the different courses also contain lots of useful information - including the structure of the year, a summary of each course, and information about exams.
The three terms at Oxford are called by different names: Michaelmas is the first term and runs from October to December, Hilary is the second term and runs from January to March, and Trinity is the third term and runs from April to June. You can find out when the terms start and finish on the main university website.
At the end of Trinity Term you will take exams - these don't count towards your final degree classification, and are simply graded distinction, pass, partial pass, or fail. You must pass these exams in order to continue with the course. You can find out more in the examinations and assessment part of the website.
Mathematics and Mathematics & Statistics students study all the courses listed below, Mathematics & Philosophy and Mathematics & Computer Science students study the courses indicated as well as Introduction to Logic and Elements of Deductive Logic, and Computer Science courses respectively