Codecademy is an online service that teaches users new programming languages, APIs, and basic web development skills. Languages it currently supports include HTML/CSS, JavaScript/jQuery, PHP, Python, and Ruby, with support for many APIs such as YouTube, GitHub, and Twitter. Through its interactive console and progress tracking, Codecademy provides examples and short exercises that constructively help you learn.
Each language has its own course track for users to follow where each step of the track is a new exercise. One of the great things about Codecademy is that instead of providing only examples for users to look at, each step requires the user to enter code themselves, which will be checked and verified by the automatic checker. Overall, Codecademy is a lot of people's first stop when trying to learn how to code or even just to pick up a new language.