Use the question to pick the source
For HTML and browser concepts, begin with MDN. For accessibility planning, the W3C Web Accessibility Initiative offers introductory resources. For a Google Search feature, use the relevant Search Central documentation rather than a secondhand summary.
Record the context
Keep the source address and the date you consulted it with your project notes. Check that instructions refer to your provider, product version and intended use. A familiar-looking screen does not establish that an old walkthrough still applies.