Usually the leader of the political party that wins a general election becomes the Prime Minister (PM for short). Their job is to come up with ideas and plans about how to run the country. They then choose the MPs who will help them run the Government. These people are called cabinet ministers. They are responsible for running different parts of the Government. The PM can have a lot of power and is held accountable for what they do by the Parliament they are answerable to. They can also be a commander-in-chief of the armed forces and make decisions about foreign intervention.
They have critical responsibilities regarding their Cabinet, they choose the cabinet members and assign them portfolios which relate to different government functions. They lead cabinet meetings and set agendas to ensure that the Cabinet works well together. They can reshuffle the Cabinet at any time and they are responsible for setting the overall direction of government policy. They also have to decide whether to use the British armed forces abroad and have ultimate responsibility for what happens in a conflict.
The Prime Minister is often viewed as having a growing role. This is often mistaken for Prime Ministerial predominance or Presidentialism, but these claims are sometimes misguided. For example, they can be based on ignorance of past debates about the nature of the Cabinet and the prime ministership that might challenge and counter claims of increasing dominance. Alternatively, they can be used as a rhetorical device, providing an easy and dramatic narrative for those who wish to criticise the style or personality of a particular prime minister.