Q&A: A guide to the European elections

What are the European elections and what are we voting for? This weekend up to 380 million people will vote across Europe to elect their representatives to the European Parliament. Of the three EU institutions – the European Council, European Commission and European Parliament – the parliament is the only institution that is directly elected by the citizens. This is the eighth such pan European election. The first direct election took place in 1979.

How many seats are up for grabs? 751. Seats are calculated through a system of "degressive proportionality" to ensure that population minnows like Malta and Ireland get more MEPs than strict proportionality would imply. As the biggest member state, Germany has 96 MEPs, while France has 75 and Italy and the UK both 73. While all countries are required to use some form of proportional representation for the elections, systems vary from country to country. Ireland is one of the few member states to use a constituency system, while a number of European countries use a list system. When will we know the outcome? The European elections are spread over four days – Britain and the Netherlands voted yesterday, while today Ireland and the Czech Republic go to the polls. The Czechs get another opportunity to vote tomorrow, along with Latvia, Malta and Slovakia, while the 21 remaining countries vote on Sunday. Results will not be announced until 10pm Irish time on Sunday when Italy becomes the last country to close its polling booths. But the final composition of the parliament will not be certain until next week, with a handful of countries including Ireland, Bulgaria and Greece slower in finalising their counts than elsewhere.

What trends should we look out for in these elections? As the first election since the euro zone crisis, polls are predicting an increase in support for populist parties of both the right and left, as austerity-weary voters express disillusionment with the European political establishment. These range from the left-wing Syriza party in Greece to the far-right Austrian Freedom Party, with an array of different political positions in between. As a result, a key trend to watch for in the weeks after the election is whether successful MEPs will be able to club together to form political groups, which play a central role in the European parliamentary process.

What do MEPs do? Despite the fact the European campaign in Ireland has been dominated by domestic issues, successful MEPs will have very little power over national issues. Instead, over the next five years, MEPs will vote on a raft of EU legislation weaving its way through the complex EU legislative system, including the EU-US trade deal, data protection rules, a new climate change and energy package and banking union. The common agricultural and fishery policies until 2020 were already agreed last year so are not likely to feature heavily.

What's all this about voters directly electing the head of the European Commission? This year, for the first time, the biggest political groups in the European Parliament have put forward candidates to become the European Commission president, a position usually decided behind closed doors. Jean-Claude Juncker, the nominee for the European People's Party (EPP) of which Fine Gael is a member and Martin Schulz of the Socialists and Democrats (S&D) to which Labour is aligned, are seen as the two candidates most likely to succeed. However, the European Council, which represents all 28 member states through their heads of Government, is lukewarm about the idea. All 28 leaders, including Enda Kenny, meet for dinner in Brussels on Tuesday to de-brief on the election, and discuss whether to accept the European Parliament's suggestion. Expect weeks of inter-institutional wrangling.