Khan Academy is a learning platform with the aim to provide “a free, world-class education for anyone, anywhere”. It offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom.
An example video from the Khan Academy:
You can choose from a great range of different subjects so you can learn about math, statistics, science, computer programming, history, art history, economics, and more. The system is adaptive, meaning that it will guide you through the materials at the right pace.