Not all information is equal! You can write a perfect paper, but if it uses the wrong information and poor sources, you're not going to get a good grade.
Evaluating sources helps determine which sources you should use and which ones you should avoid. The better your information, the better your grade!
When evaluating information, you're looking for accuracy, authority, biases, currency, intent, and relevancy. Ask yourself:
WHO created the information?
WHAT is the information about or trying to tell you?
WHERE is the information coming from?
WHEN was it published or last edited?
WHY was it written, and why would it be a good?
HOW accurate and relevant is it?