There are two ways the links can be represented in HTML: internal links refer to objects in the current directory and external to another website (source).
But how another website is defined? How does my browser actually understand which link is internal? For example,
<a href="/google.com"> this link will lead you to ./google.com file</a>
but
<a href="//google.com"> this link will lead you to the Google website</a>
So what are the general rules of distinguishing them?