Beyond the handful you use daily (&, <, ©), there's a full table of named entities plus numeric access to every Unicode code point (&#xXXXX;). Treat it as a lookup when you need a symbol that's awkward to type.
With <meta charset="utf-8"> in place, you can usually just paste the real glyph — but entities stay useful for reserved characters and when a file's encoding is uncertain. The reference is where you go to find the exact code.