Credible sources are generally understood to be accurate and reliable sources of information, free from unfair bias. The links below show a chart plotting media sources along axes of reliability and political bias. What do you think about this interpretation.
Peer review is a process scholarly articles go through before they are published. Scholarly articles are sent to other experts in the field (peers) to ensure that they contain high-quality, original research important to the field. This is a measure of quality control other types of literature don't go through.
If you can't tell whether or not a journal is peer-reviewed, check Ulrichsweb.
access the database
type in the title of the journal
peer-reviewed journals will have a referee jersey ("refereed" is another term for "peer-reviewed") - example below