Government
The government runs the country and has responsibility for developing and implementing policy and for drafting laws.
The political party that wins the most seats in a general election forms a new government, led by their party leader - who becomes Prime Minister. The Prime Minister selects the remaining Ministers. The PM and most senior Ministers make up the decision-making committee, known as the Cabinet.
Parliament
Parliament is the highest legislative authority in the UK. Parliament is made up of the House of Commons and House of Lords. It is responsible for making laws, deciding taxes and scrutinising the Government.
The House of Commons
The House of Commons comprises of Members of Parliament (MPs) that have been elected by local residents to represent an area of the country (constiituency) in Parliament. Each MP represents one constituenciy in the UK and is a member of a political party.
Full details of how Parliament and government work can be found at parliament.uk.