First identify what you're looking at, be it a personal blog, a public "ask us" site, a newspaper or blog article, a sales site, a government or non-profit website, an educational site, etc.
Then, ask yourself a few questions to evaluate the site. You can always ask a librarian or your instructor for more help!
Where is the website coming from or who is the author?
Look for clues like…
Does the website present a certain bias or specific opinion?
Look for clues like…
Can you tell when it was published?
Look for clues like…
Who is the target audience for the website?
Look for clues like…
What happens when you Google the site name, organization name, or author/founder name?
Look for clues like...
Can you fact check the information on the website?