What is copyright?
Copyright is the exclusive right of the author of a certain work to publish and duplicate such work. Such work may not be published or duplicated without permission. (Dutch Copyright Act).
It is a common misconception that copyright law does not apply to the internet. The copyright laws throughout the world clarify that making text, images, software, music or anything else protected by copyright law.
When you use content from others you have to take certain copyright restrictions/rules into account. As an author/creator you have certain rights concerning your creations.
For your own, personal study and for research, you are allowed to make a (printed or digital) copy of copyrighted work, as long as you don't share it with others.
Content could be anything you create: an article or a book, a design, photo, drawing or software programme, etc. You do not have to do anything to obtain copyright; there is no registration process as with a patent. A copyright notice (©) is therefore unnecessary. The work must however bear the stamp of the author’s personality and feature a certain degree of authenticity.
But which materials can be used in your courses, articles, papers etc.? Materials with a Creative Commons license or Public Domain. You want to know more, see Creative Commons