Many nations around the world use a type of government called a parliamentary system. In general, parliamentary systems have parliaments (or legislatures) that are either bicameral with two chambers or unicameral, where each house of parliament has its own power-sharing mechanisms.
In parliamentary democracies, legislators are elected by their constituents. Voters usually vote for parties and then the party decides how to allocate seats based on vote percentages. Typically, the majority party selects its leader to be the Prime Minister and forms a cabinet to run the country. However, if the majority party does not have a clear leader, parties may form coalitions.
Legislators also vote for laws to be passed. They can also pass a budget and call for a dissolution of the Parliament, which may require that a fresh election be held. Some parliamentary systems, such as Greece and Switzerland have strict constitutional requirements that must be met for an early election to be possible, while others, such as the Netherlands, Belgium, and Australia, allow the government to call elections at will.
The advantage of the parliamentary system is that it allows governments to respond quickly to the will of the people by calling an election or replacing its leadership. It is also easier to oust a prime minister who loses popularity, as has happened in recent times with David Cameron, Theresa May and Boris Johnson. This is because the parliamentary system does not have to wait for a constitutional process that can take years or even decades.