The years all work a little differently. In your first year you have to do at least two (one core and one optional) module in history - you could thearetically do 6 modules in the first year but they like you to take modules from outside your department in case you want to change degrees so you could pick up a language, or go into ancient history with philosophy or (as long as you have the A levels) do any extra courses that take your fancy alongside the history modules. In terms of history modules are assessed by an exam (about 50%), and a couple of essays/book reviews etc (about 33%) as well as your performance in seminars (17%)
In second year you do six modules (3 per semester). You have to do a core module in historiography covering the different schools of thought, a course assignment (like a mini dissertation, to give you some practice at the main thing before you do it next year - usually has to be linked to a module you study doesnt necessarily have to be something that you touched on in the course), a document option (I didnt do this so I have no idea what it is, they are brining it in for next year - think its more source based? not too sure.) and then three optional modules. Between your document option and three options you have to make sure you cover a medieval period, have one in an early modern and one in a modern (the other can be in any of the three period you prefer - so if you like modern history you can do two modern modules and use one of those to base your course assignment on).
Third year you can specialise in your prefered periods; you have to do a further (which you do in autumn semester, are examined on in january, and worth 1/6 of the year), one special subject (which is source based i think, you do it over the two semesters, are examined in two examinations in june and the module counts for 2/6 of the year), a dissertation (must be linked to one of the modules you are studying, in most cases the special, due in april, worth 2/6 of the year) and a core module called th uses of history (second semester, jun exam worth 75%, essay 25% - 1/6 of year).
Its more primary in the third year (though i think th document options is more about primary sources). First two years doesnt really require heavy, individual evaluation of primary sources.
In terms of exams - in first two years you'll have three modules in the first semester and an exam in january for them, and three in spring, and an exam in May/June. Exam period is three weeks long and you could theretically have your exams at any point, though mind have tended to be a week apart at most. There are topics that come up so you could get away with revising four (or maybe even three) in depth - but you need a general knowldge of the whole period covered so you'll need to briefly revise everything.
You apply for modules on the computer and you are allocated at random. You put a few choices down. You will probably find that you will get your first choice on some but not others. I'll be going into my third year and I got allocated my first choice special and second choice further. In second year allocations i got some modules i didnt want to do, so contacted the department after first year exams were realised and got to steal the place on the module i want to do that someone who had not passed the year had been allocated to; so all my modules were ones I wanted to do. There were also quite a few spaces on all but about three modules in september so you could change at that point if you wanted (i changed another one then lol, after changing my mind).
Hope that helpss!