When doing research for your own publication – a report, magazine article or book – you use existing information provided by others, both on paper and online.
This is permitted, but you can't simply include text and images by others in your own document. You have to reference the source so that the reader of your document can find your consulted sources and check that you have included the information correctly where necessary. This also gives the other person the credit they deserve. If you don't do this, you will be committing plagiarism.
By giving our source referencing a consistent style, we make them recognisable to anyone in the world. Several referencing styles exist for scientific texts – see the Reference Styles overview.
In the Netherlands the most popular reference style is APA Style, which was created by the American Psychological Association. A Dutch concise guide is available for this style.