www.cao.ieActually if you search threads for Trinity College Dublin or for studying in Ireland you'll see I've replied to them all in detail, probably saying stuff I'll forget here. Irish students are thin on the ground here!
CAO and UCAS are VERY different. CAO caters for 70,000 applicants annually. We only have 7 unis in total (plenty of other colleges and IT's etc. though). You apply online by Feb 1st, applications open in November. You can do it by paper also but not near as handy. You give your basic informationl, school and exam information. You apply by genuine order of preference- sounds like you prefer TCD, so put it first even though points will be higher. No personal statement, no predicted grades, no conditional offers. You won't recieve any info from unis as they won't know you exist. CAO give you a number, you don't go by your name. This will become you student number anyway later. You'll have several opportunities to change the order of your courses etc. throughout the year before exams, and once in the middle of June during exams.
Irish results come out on a Wednesday in the middle of June, CAO offers the Monday after. The points of a course (out of a max 600 which only about 15 people get a year) are determined by how many points the applicants for a particular course have. If a course has 30 places and the 30th person has 450 points, then these are the points for the course. (They work down from the person with the highest points). CAO make the offers and then when you accept, the uni will contact you etc. Courses that are not filled drop in the second round. Please read the CAO handbook if you're unclear on anything, you can read it on the CAO website.
You can study history in Trinity by itself (single-honour), with one other subject (TSM- two subject moderatorship) or as part of other courses- History Economics and Politics and History Philosophy and Politics. Single-honour is the least points- 460. History with Psychology is the most- 550 or so. History and English is also extremely popular- around 510. With single-honour you will do more modules. 460 is well above average, you would need AABB or higher. You will need either 4 A-Levels or 3+ an AS/A2 level (I'm not exactly clear about the second bit though). No Irish uni can accept you with just 3 subjects, home students do 7 and present 6- there's no way of equating the two otherwise. You will need a foreign language to GCSE and you cannot present some 'soft' subjects- details are on
www.tcd.ie. I'm pretty sure they are Media, General and ICT but I could be wrong.
You can't study history by itself at UCD. UCD only offers the general arts course- you have to pick two other subbjects, dropping one after 1st year but your degree will be in arts, not History like it would be in Trinity. UCD is 3 years, Trinity is 4. Arts at UCD is the biggest course in Ireland, more than 1200 places. It is a great uni but it's not in Dublin city or beside it, if that bothers you. It's about 20 mins away. I'm a bit biased as I went to Trinity.
Ask me if you want to know anything else. I went to Trinity. I did the Leaving Cert so I don't know the ins and outs of A-Levels and I commuted from home so I know a bit about accom and where would be a good place but not personal experience. I did LOADS of history modules (not a direct history student) and have to say, the lecturers are unbelievable- almost all are industry experts with loads of core books to their names and always on TV and radio clarifying stuff. Really History in Trinity is amazing.