A paid contribution is a PRSI payment - for each week you work (full-time or part-time if your income exceeds €38 pw), you pay a PRSI contribution, probably at Class A.
If you were fully unemployed at any time, you receive a credited contribution.
If you have your P60s from the years I mentioned (2011 being the important one to start with), that will tell you what class PRSI you paid, and how many contributions you paid for that year.
The PRSI year, and the relevant year for calculating illness benefit is the calendar year, so your work and contributions in 2012 would be counted separately from those in 2011.