Google Scholar was created as a tool for grouping academic literature on the web. In general, credible sources are those that can be considered unbiased and have some type of evidence to rely on. If a website is not up to date, the content is not structured, the texts contain grammatical and formatting errors; that source is probably not reliable. Students can find guidelines on how to improve their writing and academic performance in general, get useful tips to make their study process more efficient, or learn to address particular problems.
For example, if there are formatting and grammatical errors, the content isn't structured, the pages aren't loading properly, and the website isn't up to date, it's probably not reliable. If you're still not sure, you can always check if the source is present in Google Scholar or any other academic database. The suggested websites are located in the “Internet Links” tab at the top of the thematic guide page.