What is Hreflang?
Explain to me like I’m five.
You will use Hreflang if—and only if—you have multiple pages (URLs) that all have the same content translated into different languages.
These pages do not all have to be on the same domain. For example, your English content could be at https://www.example.co.uk and your Spanish content could be at https://www.example.es. Or these pages can be on different subdomains, like en.example.com and fr.example.com. You could even create separate folders for each language, e.g. www.example.com/en/foo.html and www.example.com/de/foo.html.