There are three parts to the exam. You do the Reading and Writing and the Listening papers on the same day. You may need to return to do the Speaking on a different day. You do the Speaking with two examiners and one other exam candidate.
You should take the KET if you have done more than 250 hours of study or practice and can speak, write and understand basic English. You need to ask and answer questions about yourself and others, understand announcements and instructions when people speak slowly and clearly, and tell people what you think about something you read or hear.