I think you should ask a parent/ other experienced person to help you, because all the information on this, including converting A levels to CAO points is on the CAO website.
Yes, you need to make a CAO application. UK nationals, with correct UK residency, are treated the same as the Irish.
What course? Have you checked you meet the GCSE requirements too?
Have you checked that your parents/ you can fully fund this? For at least 4 years? There are no loans, accommodation isn't guaranteed even in first year, and is in short supply and very expensive.
You'll generally need 4 excellent A levels including Maths for the most popular courses, and the points for past years (expected to go down a little next year) are also on the CAO website.
Good luck, and get help!