There are a lot of sources that you can find right now but not all of the sources that you can see are credible. Credible sources are known to be reliable sources. They are usually based on pieces of evidence or studies that other experts have spent time on.
Credible sources will make sure that the details will be backed by facts that will prove that the details that you can believe in are true. If the source is not credible, how sure are you that you are truly looking at something that is real? If you would try to discuss something and you do not back it up with sources, it can be a problem.