Three: 3 main institutions of the EU

The EU system revolves around three main institutions which have distinct roles:

European Parliament: The principal democratic component of the EU system, composed of members directly elected by Europeans. Its job is to bring the concerns and priorities of European citizens into the system and to represent their political views in accordance with the outcome of the elections.  Together with the Council, with which agreement must be found, the European Parliament is responsible for examining, amending and passing EU legislation and setting the EU's annual budget, based on proposals from the European Commission.  It also supervises the Commission, holding it to account for the way it implements EU policy and spends taxpayers' money from the EU budget.
 
Council of Ministers: The institution representing the governments of EU countries in the EU system, composed of the relevant national ministers for the subject under discussion.  Together with the Parliament, with which agreement must be found, the Council examines, amends and adopts passes EU legislation proposed by the Commission. 

European Commission: The “executive” of the EU system, the Commission is responsible for proposing new EU laws to the Parliament and the Council and for implementing those laws once passed. The Commission also implements EU policy on a day-to-day basis and manages EU programmes and actions in Europe and across the world. The Commission is composed of one commissioner from each EU country, each holding a specific policy portfolio, and is led by a President from among their number.