The difference between a tour operator and a travel agent is that the tour operators design packages within their own business and a travel agent will sell it for them. The tour or travel operator might own an airline or hotels, or could simply carry out tours etc. A travel agent does not do this.
There are a number of Irish tour operators which create package holidays abroad and in Ireland. One of the most common is ski tour operators.
Tour operators can provide everything from your accommodation, food and entertainment, to guided tours and cruises.