There is just one airport in Dublin. It has two terminals, T1 and T2. Ryanair uses the original terminal 1 while Aer Lingus is served by the newer terminal 2. There is an outdoor smoking area in T1 (Garden Terrace Bar) and Pool tables in T2 (Oak Cafe Bar). And if you're still a bit hungover from your Dublin adventure before your departure flight you can fast-track through security for €5.95 with, and it includes a free coffee! There are a number of buses to/from Dublin airport / city-centre; the Airlink 747 costs €6 with a journey time of approx. 30minutes, The Aircoach (24 hours) costs €7 & takes approx. 30 minutes while the regular Dublin bus service (number 16) costs just €3.30 but can take from 45 minutes to a little over an hour during peak times. A taxi should cost around €30-€40 depending if it's a weekend or weekday, time of day & distance.
Other airport options on the island include Shannon, Cork and Belfast, each of which serve Dublin by bus, approximately 2.5 – 3.5 hours journey.