You vote for an MP, the leader of the party with the majority goes to the King (now) and asks permission to from a government, it’s symbolic really, a formality. The leader is the PM and appoints a cabinet, seemples.
The prime minister gets to decide when to ask the monarch to dissolve parliament and hold a general election. Within their term of four years of course. parties have their own methods for electing leaders.
More HERE
PM’s question time is every Wednesday at 12:30. That’s when the fur can fly, can be very entertaining as well.