The Highway Code
The HC is key reading to explain how to use roads, whether on foot, on 2 wheels, or on 4 or more. It's the recommended text for passing the theory test, along with another two.
The HC is a guide to the law. It sets out rules so we don't conflict with each other. Its numbered paragraphs say who's responsible for what, and what's best practice to limit confusion. It includes common roadsigns and markings.
Its pictures make key points. See most of them by clicking buttons below. But don't rely on these pages instead of keeping up to date : things change. Buy The HC here or from most bookshops, and subscribe to helpful official memory-joggers.