If your application for the Ireland Working Holiday Visa is successful, you can start preparing for your journey but you have to be aware of the fact that receiving the visa does not guarantee that you will be permitted entry into Ireland.
When you arrive, you have to provide a number of documents to border officials. If they are satisfied with the information you give them, they will stamp your passport and you will be able to enter Ireland.
Then, you have to register with the Garda National Immigration Bureau to receive permission to stay in Ireland longer than 3 months.