The CAO (Central Applications Office) system in Ireland is the main way students apply for higher education courses in the Republic, after secondary school. You fill out an application form with your preferred college courses ranked in order of choice. After you get your Leaving Certificate results, the CAO uses a points system to match your scores with the course requirements. If you meet the points for your top choice and there's space available, you get an offer. If not, they move down your list until you get a match. It's important to carefully choose and rank your courses to increase your chances of getting into a programme you like.

For each grade, H1, H2, O1, O2, etc. you get awarded points. A H1 gets you 100 points, an O3 gets you 37 points and so on. There are some special cases - if you get a H6 or above in Higher Level Maths you are awarded 25 bonus points.

The exact points table is available on the CAO website here. You will find points for LCVP, foundation levels and so on. 

If I wanted to do an Honours Degree ("Bachelor of Science") in "Data Science and Artificial Intelligence" in ATU Donegal, I can see on the ATU.ie website that in 2023 the point entry requirement for the course was 296 points.  There is no guarantee that for this year it will be the same, it can move up or down depending on demand but it gives me a good idea of what to expect. 

In addition to the points, there are additional entry requirements listed - they require at least two H5 and and four subjects results of at least O6/H7 including English or Irish at O6/H7 and Mathematics at O4/H7. That sounds a bit complicated but it will be broken down for you in class and in your career appointments. 

Courses are listed in detail on each third level institutions website (e.g. ATU.ie) usually under 'Undergraduate Courses' or similar. Alternatively you can also search for courses by keywork on the CAO.ie website. Here's their search engine, try it out.