Critical thinking and evaluation are important because they focus on public evidence and challenge blind authority and individual bias.
Critical evaluation means careful and exact thinking. It means looking for public forms of evidence rather than simply accepting what we are told or our own biased intuitions.
Some things to consider in evaluating all types of sources*:
Currency: Is the information current and up-to-date?
Relevance: Does the information have anything to do with your topic?
Authority: Is it authoritative? Who wrote it? A scholar writing an article about his/her field is very authoritative. Politicians, news reporters, bloggers, etc, will need to be fact-checked against authoritative sources to ensure they are relaying facts in an unbiased way.
Accuracy: Is reliable and true? Check their references! Do they cite where they found the information? If so, is that source trustworthy? If not, can you find other sources that support their facts?
Purpose: Why does the information exist? This is a big clue as to whether it could be biased or not. Advertisements intend to sell, politicians want your vote, Facebook posts want you to "share," Non-profits want to raise money. That doesn't mean they are always all lying but going on a knee-jerk reaction often isn't best.
Check the acronym. Did your website pass the CRAAP Test?!
*Criteria adapted from the CRAAP Test, Meriam Library, California State University, Chico