On the internet a wide range of digital learning materials can be found in various resources, such as YouTube, Khan Academy or from other publishers. Some are specifically designed with an educational aim, others are more general. Also quality differs from professional to amateurish productions. Different license forms (open or closed) make use and re-use of existing materials possible in different ways. If you see a Creative Commons logo, you can be quite sure that you will be able to (re)use it.
You can find much more informaton and guidance via Digital Learning Resources.