There are various legal structures available the most common being a sole trader, partnership and a limited company. If you are an individual who would like to start selling products or provide a service your best option is a sole trader. The benefit being it is easy to setup and there is less administration. However, please note you are personally liable for any losses. However, with a limited company your losses are limited to what you invest.
A sole trader is an individual who sells products and services. You can hire staff and rent premises. If you are planning to work as a sole trader you need to notify Revenue and register as a sole trader. You do not need to register for VAT until reach certain thresholds. If you are trading using a name other than your own you need to register that business name with the CRO.
If you would like to setup a separate legal entity you need to do so with the CRO. You can setup a one person company but you need one other person to be the chairman. The process is very straight forward. The CRO provide you with all the documentation you need and the filing fee is €50. Like a sole trader if you are trading under a different name than your legal entity name you need to register this business name with the CRO. All of this can be completed on www.core.ie
If you setup a limited company please do not forget to complete your annual return. Failing to do so will mean you will lose your audit exemption. The cost of having you accounts audited even for a shell company with no transactions can cost up to €2,500.