The test is computer based and contains 24 questions and is designed to test applicant's knowledge of life in the UK in 45 minutes time.
Everybody in the age of 18-64 is required to pass this test as part of their citizenship application process since 2005 exept of some disabled.
You need to pass the test once – you don't need to pass the test again if you became a British citizen and previously passed for settlement needs.
You must score 75% or more to pass the test. This is equivalent to answering 18 or more out of 24 questions correctly. Pretty simple rule isn't it.