Im confused about the The united kindom and how it works?

Alright so Im a dumb american I guess, I dont understand I always thought everyone who had a british accent were from a country called england.... But recently i herd of like, Wales, great britain, and the UK. I thought they were all citys in england.. I dont understand and what is Ireland and Scottland there there own countrys so why are they called UK! I do not understand im so confused! Who rules over there? i thought it was Queen Elizabeth but then I herd they have a prime minister... So wth someone fill me in please !