Why evaluate?
It's important to evaluate all information sources for reliability and credibility -- but especially web sources, because almost anybody can put content on the web.
Using quality sources shows your professors, fellow students, and other readers that you have done your research and know what you are talking about.
How to evaluate?
An easy way to evaluate sources is to think of a journalist's questions: who, what, when, where, why, and how. Think about questions like these for each of your sources:
Who made this? 
- Who is the author?
- What is their academic training, life experience, or some other skill set that makes them knowledgeable about this subject?
- Look for an About Us page (especially so if there is no author name). With what organizations is this site affiliated?
- If it is attributed to an organization or department (e.g., Department of Justice, Pew Institute, American Medical Association), what is its authority on the topic?
What is in it? 
- Is it relevant and sufficiently detailed to support your area of study? How can you tell?
- Are there references to other sources that back up what the author says? What kinds of other sources are they -- are they all from the same ideological "side?
- What type of evidence is provided? Is it discussed fairly, or is the author cherry-picking certain facts or taking things out of context? How can you tell that the author considered all sides of the issue, and not just her preconceived ideas?
- Is it logical? Well-written? Grammatically solid?
When was it made? 
- When was it first published? Last updated? Are there newer editions or versions?
- How much has changed in this field since the publication date?
- If it's an older source, is it useful to view for historic reasons? Or do you need current info?
- Are there more recent reviews, responses, or rebuttals to it, and how might that change the original's argument?
Where was it made? 
- Look for a Mission, Vision, or About Us page.
- Is it affiliated with an organization of some sort?
- A university or school (often .edu)
- State, local, or national government (often .gov)
- Non-profit or religious organization, interest group, political party, club, museum, etc. (often, but not always, .org)
- Some of these may be credible, but others may have a bias or an obvious agenda to promote. What is their reason for existing and sharing this information?
Why was it made?
- To inform? To persuade? To entertain? To make money? (Be suspect of clickbait-y or social media-only stories here)
- Who has financial interest in this content? Who is making money off of it, and how?
- Look for advertisements for a clue. "Sponsored content," "Recommended content," "You might also like," and other similar links also mean those are paid ads!
- Look for funding agencies for foundations or scholarly research. For example, in the now-discredited study that linked autism to vaccines, it was later proven that the researcher, Andrew Wakefield, was being paid by lawyers who wanted to sue vaccine manufacturers -- a clear conflict of interest that should have been revealed.
How was it made? 
- Did it go through the peer-review process -- a process by which other experts in the field review and quality-check the research before publication?
- If not, is there evidence of other editorial review, such as an editorial board, a single editor, or no editor?
- How much was it updated or corrected after publication? NewsDiffs.org is a great site for tracking corrections or additions to popular news articles.
- How is it vetted and reviewed by editors? Is it written with the intent to be factual reporting or strictly "Opinion" (a.k.a. "Contributors," "Commentary," "Other voices," or other terminology)?
