If I get on a bus to Dublin, it usually stops at a stop near the centre or you can hang on and go all the way down to Busaras.
What I'm wondering is, how do I get to the RDS ?.
Should I go back to the train station and get a Luas or how does it work exactly?.
Any help appreciated?.
It depends on where you are coming from, a significant detail you've omitted. Anyway, from the centre of the city there are a lot of buses that go to the RDS from the city centre. 5, 7, 7A, 8, 45, 63 and 84 being the main ones. Any bus going to Ballsbridge, which is where the RDS is, will do. Check out the Dublin Bus website for timetables for the above routes, and where you can get them. They all go from the city centre, not far from Busaras. The other alternative is to get the DART from Connolly station to Lansdowne Road station.
Sandymount would be better if you're heading for RDS Simmonscourt
yes the no. 7 bus is the best choice, you can get it outside ulster bank opposite supermacs in o connell street southbound and get off at the horseshoe pub in ballsbridge, or as already mentioned get the dart southbound to sandymount and turn right and cross the level crossing and head to end of this road and turn right at the end where the rds will be more or less opposite