What is the difference between external and internal links?

External links point outside the current document (usually with a full URL); internal links jump within the same page using # plus an element's id.

An external link sends the user to a separate document — typically on another site — so it carries a full URL including the protocol (https://):

<a href="https://www.hslu.ch">HSLU Website</a>

An internal link stays on the same page and scrolls to a specific spot. You mark the target with an id attribute and reference it with # followed by that id:

<a href="#chapter1">Jump to Chapter 1</a>
...
<h2 id="chapter1">Chapter 1</h2>

The mechanics to remember:

• The link's href is # plus the target's id value.
• That id must be unique within the document, since it names one exact location.
• Clicking scrolls the page to the element bearing that id (any element can have an id, not just headings).

This powers familiar patterns like a table of contents, "back to top" links, and navigation within a long single-page document.