A great way to establish the credibility of a source is to go through the ABC's. A: authenticity, B: bias, C: content.
When it comes to establishing authority, you are evaluating the person(s) who created the source you want to use. What authority do they have to make the claims they do? One of the ways to verify authority is to look at where the source comes from. Is it very clearly a blog post or opinion piece? Is it a social media post? These kinds of sources are difficult to authenticate and are therefore not reliable. But is it in a journal you have access to through the library? Did you find it on one of the library's databases? (Sensing a pattern?)
The best way to make sure you're finding a reliable source is by using the library resources!
Bias is arguably unavoidable when it comes to anything produced by humans. However, scholarly sources have different systems set up to try and eliminate bias. One of these ways (and therefore one of the ways you can verify a reliable source) is through peer-review. This process means that a journal or book has been read and edited by multiple professionals in a given field before it gets published. Knowing where a source comes from will tell you if it requires peer review before publishing. Once you know the publisher, you can Google whether they require peer reviews.
Finally, the content of an article, or in other words, what it says, can also give you a good idea of how reliable it is. Scholarly sources will have a certain tone and they will usually have in-text citations throughout the paper that lead to the list of sources at the end. They won't include a lot of opinions and will be written in a way that feels informative, as opposed to click-bait.
Is there an obvious bias behind the article?
Does the source feel emotionally-driven rather than fact-based?
Can I trust the author or creators of the source? Can I identify them?
Do they cite other work within their work? (this does not include inserted links)