You need to make sure that the information you use in assignments will help you gain marks, not lose them!
The following links will help you decide whether the information you are looking at is suitable and reliable:
Bob and a cat at the Open University suggest you ask who, why and where before trusting what you read online
A bit more detail on the questions to ask from Oxford Brookes University
If you prefer a flow chart to take you through the process this one is from Cardiff University