The voting system used to elect MPs to the UK Parliament is called First Past the Post (FPTP).
The FPTP electoral system is used to elect MPs to the House of Commons. For the purpose of the election, the UK is divided into 650 areas or constituencies (seats) and at the election the candidate with the most votes becomes the MP.
In addition to voting for a local MP, voters are also taking part in choosing a government. The party with the most MPs becomes the government. In 2015, the Conservatives had more MPs than all the other parties put together (a majority of the MPs) so they became the government.
In 2010, unusually,no party won a majority of the MPs (had more MPs than all the other parties put together) so the Conservative Party (the largest party after the election) invited the Liberal Democrat Party to share power in a coalition government.